In FE 7 modules, I've edited "Character List.txt" in "Chapter Unit Editor" module. I first just tried to just add a new name, but it wouldn't even show up. But I saw that the number of names (256 total) were written in hexadecimals. So I just changed the total number to 257, and added the custom name at the bottom of the list.
I did the same to "FE 7 Character List.txt" in the "Class & Character Editor" module.
I barely know what I'm doing actually. :P
It seems easier to change an existing character right now, than to make a new one. Even though I just copied most of existing characters anyway.