Structure I plan to try, when I have time to code it up:

Catalogue a list of frames that are already edit mode supported.

In functions like Register Hideable, Register Resizable, etc, check if it is a preexisting frame. First time registering one, store it in a separate DB.

When one is selected, open the EME dialog box next to the existing dialog box. Do not try to interfere with the existing dialog box.

Put the calls to Register Hideable, etc, in the main addon lua, not in the library.