I don't know wether companion editing comes from the mod or is also in vanilla. Never played Bannerlord without the linked mod, it is great. Anyway, you right click in the Party Window on a character and then can edit his/her appearance and change the name from the opening window.
I would advice in addition an (awesome) mod for character export/import, to have control over the quite often weird/useless companion abilities/skills:
https://www.nexusmods.com/mountandblade2bannerlord/mods/16?tab=description