Still doing missions: custom characters in bar

I was trying to place a custom character (that I added to costumes.ini) into a bar, so that you can select it and it offers you a mission with an Accept/Reject tab. So it appears that it only accepts nicknames of very specific costume entries, and the rest cause a crash.

Do I have to add them to some kind of list that exists in the game files? Or is it something deeply implanted in the game?

Actually, I was talking about storyline characters. I found a file called "spacific_npc.ini" which is responsible for this issue, all I had to do is to add the costume name to the entry.

But thanks for the info, it'll help me in the future with custom factions