I hope this will help you (sr because i can't speak English )
I'm afraid that does not influence the selection of character, .bcs file is the script file from character, and .amk what I'm not clear yet . but which does not affect the character selection, that doing mods I have ever confused me and I put the other character and not load the character in selection menu or not load to enter a battle or mission.
I think we will be more complicated than we think.
After doing some tests yesterday, I think I know why the box is not unlocked if we put a new character.
The fact is that, besides the absence of the "XXX_000.emb" file within CHARA01.emb
Not only that, I guess even you put the character in the side missions to unlock it (although I do not think it takes as Jaco is unlocked only without missions, same as SSGSS Vegeta, Goku SSGSS and Frieza Gold.).
The game requires an ID to recognize it within the custom_skill file aura_setting, character_name, and know how many slots have the space from new character. this has to have another section to allocate the skins have each character, not only indicating the file .BCS each character. The interface needs to indicate that load on each slot char, char 000, char001, char002, etc ..
although it is true that this logic dismisses me when I try to add Demigra both CHARASELE.iggy, as in Time Patrol Quest. Demigra is in all the above points (except CHARA01.emb file). but when I try to add it, for some reason the game crashed.
I don't know if this will help but I think CHARA01.EMB has something to do with it, when I use the original one from before the DLC packs, all the icons in the select menu went gray and there seemed to be an infinite amount of them. I think that in order to unlock a character for use in the selection menu, it needs a listing in CHARA01.EMB, a listing in all files that have the character codes (for example every GOK would have to be replaced with ABC in order to add it), and for it to be linked to a quest. Then have the save file list that quest as completed. I think we need to focus more on how to modify or add quests, then link ABC to a created quest/modified quest to add ABC. Just an idea. I have no experience compared to you guys so what I'm saying could easily be horseshit. I don't know. Just throwing this out there.