diff --git a/datalad_next/annexremotes/__init__.py b/datalad_next/annexremotes/__init__.py
index 06eeca02..d260838f 100644
--- a/datalad_next/annexremotes/__init__.py
+++ b/datalad_next/annexremotes/__init__.py
@@ -4,6 +4,7 @@
 # in a single place
 from annexremote import UnsupportedRequest
 from typing import Any
+from os import environ
 
 from datalad.customremotes import (
     # this is an enhanced RemoteError that self-documents its cause
@@ -32,9 +33,20 @@ def repo(self) -> LeanAnnexRepo:
         to limit further proliferation of the ``AnnexRepo`` API.
         """
         if self._repo is None:
-            self._repo = LeanAnnexRepo(self.annex.getgitdir())
+            self._repo = LeanAnnexRepo(self.repodir)
         return self._repo
 
+    @property
+    def repodir(self) -> str:
+        import sys
+        repodir = self.annex.getgitdir()
+        # git-annex also sets GIT_DIR, and we want to account for that
+        # to be able to run regular Git command in this environment
+        gitdir_env = environ.get("GIT_DIR")
+        if gitdir_env and repodir.endswith(gitdir_env):
+            repodir = repodir[:-len(gitdir_env)]
+        return repodir
+
     @property
     def remotename(self) -> str:
         """Name of the (git) remote the special remote is operating under"""
diff --git a/datalad_next/annexremotes/archivist.py b/datalad_next/annexremotes/archivist.py
index 7696f121..a10a0c19 100644
--- a/datalad_next/annexremotes/archivist.py
+++ b/datalad_next/annexremotes/archivist.py
@@ -162,7 +162,7 @@ def prepare(self):
         # us a `LeanAnnexRepo`.
         # TODO it is unclear to MIH what is actually needed API-wise of the legacy
         # interface. Needs research.
-        self._repo = LegacyAnnexRepo(self.annex.getgitdir())
+        self._repo = LegacyAnnexRepo(self.repodir)
         # are we in legacy mode?
         # let remote-specific setting take priority (there could be
         # multiple archivist-type remotes configured), and use unspecific switch
diff --git a/datalad_next/config/default.py b/datalad_next/config/default.py
index b77eb2c2..33d95f66 100644
--- a/datalad_next/config/default.py
+++ b/datalad_next/config/default.py
@@ -82,7 +82,7 @@ def legacy_register_config(
     title: str,
     *,
     default: Any = UnsetValue,
-    default_fn: Callable | type[UnsetValue] = UnsetValue,
+    default_fn: Callable | None = None,
     description: str | None = None,
     type: Constraint | None = None,  # noqa: A002
     dialog: str | None = None,
@@ -99,7 +99,6 @@ def legacy_register_config(
         ),
         store_target=get_store_target_from_destination_label(scope),
     )
-
     # lastly trigger legacy registration
     _legacy_register_config(
         name=name,
diff --git a/datalad_next/config/git.py b/datalad_next/config/git.py
index ec67688c..fd97b614 100644
--- a/datalad_next/config/git.py
+++ b/datalad_next/config/git.py
@@ -8,6 +8,7 @@
 from os import name as os_name
 from typing import (
     TYPE_CHECKING,
+    Hashable,
 )
 
 if TYPE_CHECKING:
@@ -22,7 +23,7 @@
 from datasalad.runners import CommandError as SaladCommandError
 from datasalad.settings import CachingSource
 
-from datalad.consts import DATASET_CONFIG_FILE
+from datalad.consts import DATASET_CONFIG_FILE  # type: ignore
 
 from datalad_next.config.item import ConfigurationItem
 from datalad_next.runners import (
@@ -93,33 +94,30 @@ def load(self) -> None:
         # the "blobs" is known
         self._sources = origin_paths.union(origin_blobs)
 
+        setter = '__setitem__'
         for k, v in dct.items():
-            if isinstance(v, tuple):
-                vals = tuple(
-                    ConfigurationItem(
-                        value=val,
-                        store_target=self.__class__,
-                    )
-                    for val in v
-                )
-            else:
-                vals = ConfigurationItem(
-                    value=v,
+            if not isinstance(v, tuple):
+                v = (v,)
+            for val in v:
+                item = ConfigurationItem(
+                    value=val,
                     store_target=self.__class__,
                 )
-            super().__setitem__(k, vals)
+                getattr(super(), setter)(k, item)
+                # for every subsequent value we must call add()
+                setter = 'add'
 
 
-    def __setitem__(self, key: str, value: Setting) -> None:
+    def __setitem__(self, key: Hashable, value: Setting) -> None:
         call_git(
-            [*self._get_git_config_cmd(), '--replace-all', key, str(value.value)],
+            [*self._get_git_config_cmd(), '--replace-all', str(key), str(value.value)],
             capture_output=True,
         )
         super().__setitem__(key, value)
 
-    def add(self, key: str, value: Setting) -> None:
+    def add(self, key: Hashable, value: Setting) -> None:
         call_git(
-            [*self._get_git_config_cmd(), '--add', key, str(value.value)],
+            [*self._get_git_config_cmd(), '--add', str(key), str(value.value)],
             capture_output=True,
 
         )
@@ -145,35 +143,48 @@ def _get_git_config_cwd(self) -> Path:
 class LocalGitConfig(GitConfig):
     def __init__(self, path: PathLike):
         super().__init__()
-        self._path = path
+        pathobj = Path(path)
+
         try:
-            self._is_bare_repo = call_git_oneline(
-                ['rev-parse', '--is-bare-repository'],
-                cwd=path,
+            #TODO CHECK FOR GIT_DIR and adjust
+            self._in_worktree = call_git_oneline(
+                ['rev-parse', '--is-inside-work-tree'],
+                cwd=pathobj,
                 force_c_locale=True,
             ) == 'true'
-        except CommandError:
-            # TODO: this is too simplistic. It could also be
-            # that there is no repo (yet)
-            self._is_bare_repo = False
+        except CommandError as e:
+            from os import environ
+            msg = f"no Git repository at {path}: {e!r} {environ.get('GIT_DIR')}"
+            raise ValueError(msg) from e
+
+        self._gitdir = Path(
+            path if not self._in_worktree
+            else call_git_oneline(
+                ['rev-parse', '--path-format=absolute', '--git-dir'],
+                cwd=pathobj,
+                force_c_locale=True,
+            )
+        )
 
     def _get_git_config_cmd(self) -> list[str]:
-        return ['-C', str(self._path), 'config', '--local']
+        return ['--git-dir', str(self._gitdir), 'config', '--local']
 
     def _get_git_config_cwd(self) -> Path:
-        return self._path
+        # we set --git-dir, CWD does not matter
+        return None
 
 
 class DataladBranchConfig(LocalGitConfig):
     def __init__(self, path: PathLike):
         super().__init__(path)
+        self._path = path
 
     def _get_git_config_cmd(self) -> list[str]:
         return [
-            '-C', str(self._path),
-            'config',
-            *(('--blob', 'HEAD:.datalad/config') if self._is_bare_repo else
-              ('--file', str(self._path / DATASET_CONFIG_FILE))),
+            '--git-dir', str(self._gitdir), 'config',
+            *(('--file', str(self._path / DATASET_CONFIG_FILE))
+              if self._in_worktree
+              else ('--blob', f'HEAD:{DATASET_CONFIG_FILE}'))
         ]
 
     def _ensure_target_dir(self):
@@ -182,11 +193,11 @@ def _ensure_target_dir(self):
             custom_file = Path(cmd[cmd.index('--file') + 1])
             custom_file.parent.mkdir(exist_ok=True)
 
-    def __setitem__(self, key: str, value: Setting) -> None:
+    def __setitem__(self, key: Hashable, value: Setting) -> None:
         self._ensure_target_dir()
         super().__setitem__(key, value)
 
-    def add(self, key: str, value: Setting) -> None:
+    def add(self, key: Hashable, value: Setting) -> None:
         self._ensure_target_dir()
         super().add(key, value)
 
@@ -224,10 +235,7 @@ def _proc_dump_line(
         # man git-config:
         # just name, which is a short-hand to say that the variable is
         # the boolean
-        #v = "true"
-        # BUUUUUT datalad of old want it to stay `None`
-        # BUUUUUUUUT it also want it to be reported as True later on
-        v = None
+        v = "true"
     # multi-value reporting
     present_v = dct.get(k)
     if present_v is None:
diff --git a/datalad_next/config/gitenv.py b/datalad_next/config/gitenv.py
index 1d091ae4..fb434474 100644
--- a/datalad_next/config/gitenv.py
+++ b/datalad_next/config/gitenv.py
@@ -60,7 +60,7 @@ def getall(
         default: Any = None,
     ) -> tuple[Setting, ...]:
         try:
-            val = get_gitconfig_items_from_env()[key]
+            val = get_gitconfig_items_from_env()[str(key)]
         except KeyError:
             return (self._get_default_setting(default),)
         vals = val if isinstance(val, tuple) else (val,)
diff --git a/datalad_next/config/item.py b/datalad_next/config/item.py
index f2ae5510..9d883cb8 100644
--- a/datalad_next/config/item.py
+++ b/datalad_next/config/item.py
@@ -14,7 +14,6 @@
     from datasalad.settings import Source
 
     from datalad_next.config import (
-        Dialog,
         dialog as dialog_collection,
     )
     from datalad_next.constraints import Constraint
@@ -60,7 +59,7 @@ def __init__(
         self._store_target = store_target
 
     @property
-    def dialog(self) -> Dialog | None:
+    def dialog(self) -> dialog_collection.Dialog | None:
         return self._dialog
 
     @property
diff --git a/datalad_next/config/legacy.py b/datalad_next/config/legacy.py
index 80693d67..fb66cdf5 100644
--- a/datalad_next/config/legacy.py
+++ b/datalad_next/config/legacy.py
@@ -59,6 +59,37 @@ def wrapper(*args, **kwargs):
     return wrapper
 
 
+class LegacyOverridesProxy:
+    """Proxy class to wrap the legacy ConfigManager overrides
+
+    There were handed out for direct manipulation of their holding
+    dict. This allowed for arbitrary modification. This class is
+    supposed to give us a fighting change to keep supporting this
+    interface, while being able to issue deprecation warnings
+    and continue to integrate with the new setup.
+
+    For now this wraps the legacy-override source, but it could
+    eventually migrate to read from and write to the git-command
+    source.
+    """
+    def __init__(self, overrides: InMemory):
+        self._ov = overrides
+
+    def items(self):
+        for k, v in self._ov._items.items():
+            yield k, v.value if not isinstance(v, tuple) \
+                else (i.value for i in v)
+
+    def update(self, other):
+        for k, v in other.items():
+            self._ov._items[k] = self._ov.item_type(v) \
+                if not isinstance(v, tuple) \
+                else tuple(self._ov.item_type(i) for i in v)
+
+    def copy(self):
+        return dict(self.items())
+
+
 class ConfigManager:
     def __init__(
         self,
@@ -76,8 +107,7 @@ def __init__(
             source=source,
         ))
         self._defaults = manager.sources['defaults']
-        for src in self._mngr.sources.values():
-            src.load()
+        self.reload()
 
         # TODO: make obsolete
         self._repo_dot_git = None
@@ -93,10 +123,10 @@ def __init__(
 
     @property
     def overrides(self):
-        # this is a big hassle. the original class hands out the real dict to do any
-        # manipulation with it. for a transition we want to keep some control, and
-        # hand out a proxy only
-        return MappingProxyType(self._mngr.sources['legacy-overrides']._items)
+        # this is a big hassle. the original class hands out the real dict to
+        # do any manipulation with it. for a transition we want to keep some
+        # control, and hand out a proxy only
+        return LegacyOverridesProxy(self._mngr.sources['legacy-overrides'])
 
     @property
     def _stores(self):
@@ -114,7 +144,10 @@ def _stores(self):
         return {'git': {'files': files}}
 
     def reload(self, force: bool = False) -> None:
-        for s in self._mngr.sources.values():
+        for n, s in self._mngr.sources.items():
+            if n in ('legacy-overrides', 'defaults'):
+                continue
+            s.reinit()
             s.load()
 
     def obtain(self, var, default=None, dialog_type=None, valtype=None,
@@ -187,7 +220,7 @@ def _obtain_from_user(
         **kwargs,
     ):
         # now we need to try to obtain something from the user
-        from datalad.ui import ui
+        from datalad.ui import ui  # type: ignore
 
         if (not ui.is_interactive or default_item.dialog is None) and default is None:
             raise RuntimeError(
@@ -387,6 +420,8 @@ def unset(self, var, scope='branch', reload=True):
             src.load()
 
     def get_src(self, scope):
+        if scope is None:
+            scope = 'local'
         name = scope_label_to_source_label_map.get(scope)
         if name is None:
             raise ValueError(f'unknown scope {scope!r}')
@@ -427,7 +462,7 @@ def get_sources(
       and 'branch-local'.
     """
     nodataset_errmsg = (
-        'ConfigManager configured to read from a branch of a dataset only, '
+        'ConfigManager configured to read from (a branch of) a dataset, '
         'but no dataset given'
     )
     # if applicable, we want to reuse the exact same source instances as the
@@ -450,7 +485,7 @@ def get_sources(
             'datalad-branch': DataladBranchConfig(dataset.pathobj),
         }
     if source == 'local':
-        if not dataset:
+        if dataset is None:
             return {
                 'legacy-environment': global_sources['legacy-environment'],
                 'legacy-overrides': ovsrc,
@@ -465,6 +500,8 @@ def get_sources(
             'git-system': global_sources['git-system'],
         }
     if source == 'branch-local':
+        if dataset is None:
+            raise ValueError(nodataset_errmsg)
         return {
             'legacy-overrides': ovsrc,
             'git-local': LocalGitConfig(dataset.pathobj),
@@ -492,11 +529,6 @@ def get_sources(
 
 
 def anything2bool(val):
-    if val is None:
-        # TODO: just changes this behavior
-        # forced by a test in old core that forces _proc_dump_line
-        # to work this way
-        return True
     if val == '':
         return False
     if hasattr(val, 'lower'):
@@ -568,4 +600,4 @@ def rewrite_url(cfg, url):
 
 
 # for convenience, bind to class too
-ConfigManager.rewrite_url = rewrite_url
+ConfigManager.rewrite_url = rewrite_url  # type: ignore
diff --git a/datalad_next/config/manager.py b/datalad_next/config/manager.py
index ca94c14a..d84b17ed 100644
--- a/datalad_next/config/manager.py
+++ b/datalad_next/config/manager.py
@@ -1,4 +1,11 @@
-from datasalad.settings import Settings
+from __future__ import annotations
+
+from contextlib import contextmanager
+from typing import Generator
+from datasalad.settings import (
+    Settings,
+    UnsetValue,
+)
 
 from datalad_next.config.default import ImplementationDefault
 from datalad_next.config.env import LegacyEnvironment
@@ -20,3 +27,31 @@ def __init__(self, defaults: ImplementationDefault):
             'git-system': SystemGitConfig(),
             'defaults': defaults,
         })
+
+    @contextmanager
+    def overrides(self, overrides: dict) -> Generator[ConfigManager]:
+        """Context manager to temporarily set configuration overrides
+
+        Internally, these overrides are posted to the 'git-command' scope,
+        hence affect the process environment and newly spawn subprocesses.
+
+        .. todo::
+
+           ATM this implementation cannot handle multi-value settings.
+           Neither as incoming overrides, nor as to-be-replaced existing
+           items.
+        """
+        gitcmdsrc = self.sources['git-command']
+        restore = {}
+        # TODO: handle multivalue settings
+        for k, v in overrides.items():
+            restore[k] = gitcmdsrc.get(k, gitcmdsrc.item_type(UnsetValue))
+            gitcmdsrc[k] = gitcmdsrc.item_type(v)
+        try:
+            yield self
+        finally:
+            for k, v in restore.items():
+                if v.pristine_value is UnsetValue:
+                    del gitcmdsrc[k]
+                else:
+                    gitcmdsrc[k] = v
diff --git a/datalad_next/config/tests/test_core.py b/datalad_next/config/tests/test_core.py
index 666d324e..a76bae76 100644
--- a/datalad_next/config/tests/test_core.py
+++ b/datalad_next/config/tests/test_core.py
@@ -145,13 +145,15 @@ def test_something(path=None, new_home=None):
         [(u'onemore.complicated の beast with.dot.findme', '5.0'),
          ('something.empty', ''),
          ('something.myint', '3'),
-         ('something.novalue', None),
+         # no-value is a shorthand for 'true'
+         ('something.novalue', 'true'),
          ('something.user', ('name=Jane Doe', 'email=jd@example.com'))])
     assert_equal(
         sorted(cfg.items('something')),
         [('something.empty', ''),
          ('something.myint', '3'),
-         ('something.novalue', None),
+         # no-value is a shorthand for 'true'
+         ('something.novalue', 'true'),
          ('something.user', ('name=Jane Doe', 'email=jd@example.com'))])
 
     # by default get last value only
@@ -167,7 +169,8 @@ def test_something(path=None, new_home=None):
     assert_equal(cfg.getbool('something', 'myint'), True)
     # git demands a key without value at all to be used as a flag, thus True
     assert_equal(cfg.getbool('something', 'novalue'), True)
-    assert_equal(cfg.get('something.novalue'), None)
+    # no-value is a shorthand for 'true'
+    assert_equal(cfg.get('something.novalue'), 'true')
     # empty value is False
     assert_equal(cfg.getbool('something', 'empty'), False)
     assert_equal(cfg.get('something.empty'), '')
diff --git a/datalad_next/config/utils.py b/datalad_next/config/utils.py
index c605ded1..03b692fc 100644
--- a/datalad_next/config/utils.py
+++ b/datalad_next/config/utils.py
@@ -2,13 +2,12 @@
 
 from os import environ
 from typing import (
-    Dict,
     Mapping,
     Tuple,
 )
 
 
-def get_gitconfig_items_from_env() -> Mapping[str, str | Tuple[str, ...]]:
+def get_gitconfig_items_from_env() -> dict[str, str | Tuple[str, ...]]:
     """Parse git-config ENV (``GIT_CONFIG_COUNT|KEY|VALUE``) and return as dict
 
     This implementation does not use ``git-config`` directly, but aims to
@@ -29,7 +28,7 @@ def get_gitconfig_items_from_env() -> Mapping[str, str | Tuple[str, ...]]:
       times, the respective values are aggregated in reported as a tuple
       for that specific key.
     """
-    items: Dict[str, str | Tuple[str, ...]] = {}
+    items: dict[str, str | Tuple[str, ...]] = {}
     for k, v in ((_get_gitconfig_var_from_env(i, 'key'),
                   _get_gitconfig_var_from_env(i, 'value'))
                  for i in range(_get_gitconfig_itemcount())):
diff --git a/datalad_next/iter_collections/tests/test_iterannexworktree.py b/datalad_next/iter_collections/tests/test_iterannexworktree.py
index 2a767a43..bdb99369 100644
--- a/datalad_next/iter_collections/tests/test_iterannexworktree.py
+++ b/datalad_next/iter_collections/tests/test_iterannexworktree.py
@@ -2,10 +2,9 @@
     PurePath,
 )
 
-from datalad import cfg as dlcfg
+from datalad_next.config import manager
 
 from datalad_next.datasets import Dataset
-from datalad_next.utils import check_symlink_capability
 
 from ..gitworktree import (
     GitTreeItemType,
@@ -17,13 +16,9 @@
 
 
 def _mkds(tmp_path_factory, monkeypatch, cfg_overrides):
-    with monkeypatch.context() as m:
-        for k, v in cfg_overrides.items():
-            m.setitem(dlcfg.overrides, k, v)
-        dlcfg.reload()
+    with manager.overrides(cfg_overrides):
         ds = Dataset(tmp_path_factory.mktemp('ds')).create(
             result_renderer='disabled')
-    dlcfg.reload()
     return ds
 
 
diff --git a/datalad_next/patches/replace_ora_remote.py b/datalad_next/patches/replace_ora_remote.py
index 952d0845..9a2dc0f8 100644
--- a/datalad_next/patches/replace_ora_remote.py
+++ b/datalad_next/patches/replace_ora_remote.py
@@ -41,7 +41,6 @@
 from datalad.config import anything2bool
 from datalad.customremotes import (
     ProtocolError,
-    SpecialRemote,
 )
 from datalad.distributed.ora_remote import (
     HTTPRemoteIO,
@@ -61,6 +60,7 @@
     verify_ria_url,
 )
 from datalad.utils import on_windows
+from datalad_next.annexremotes import SpecialRemote
 
 from . import apply_patch
 
@@ -229,7 +229,7 @@ def _load_local_cfg(self):
 
         # this will work, even when this is not a bare repo
         # but it is not capable of reading out dataset/branch config
-        self._repo = AnnexRepo(self.gitdir)
+        self._repo = AnnexRepo(self.repodir)
 
         cfg_map = {"ora-force-write": "force_write",
                    "ora-ignore-ria-config": "ignore_remote_config",
@@ -723,7 +723,7 @@ def push_io(self):
     def prepare(self):
 
         gitdir = self.annex.getgitdir()
-        self._repo = AnnexRepo(gitdir)
+        self._repo = AnnexRepo(self.repodir)
         self._verify_config()
 
         self.get_store()