Can't seem to change the portal Trigger items

[Winddbourne]

Perhaps I am missing something obvious but I can't seem to find a way to alter which item is needed for the portal when entering different cavern dimensions.

Specifically I want to make the Cavern dimension my BASIC mining area. I've lowered sea level and land generation height making the over world run much more smoothly and thus allowing for more interesting world generation there as well . . . and along with that I've disabled caves/mineshafts/dungeons plus most ore generation. Emeralds should still generate in extreme hills but I don't want players to have to find one BEFORE they start their first basic foray into the mines. lol