Each of the releases has a link in the description which points to the given config in the firmware editor. You can then make changes and saved them and create a custom link like that as well – I believe it's done by clicking on the floppy disk icon.
A layout editor for TADA68.
If you're on a Mac, you'll need to clean up the files on the TADA68 after copying the new FLASH.bin file.
TADA68 Keyboard Fireware Editor (broken)
The original layout editor written in Flash. It no longer works, see #3.
Even if you choose the English translation, not all elements of the UI are going to be translated. This post explains the options for the Fn button.