I have heard a multitude of times that you could use wrye bash to give certain races certain identities. Example: I am making a race of Dunmer except with a beard but noone addresses me as such. I use this technique so that I will be addressed properly as a dunmer.

OBSE's SetRaceAlias allows you to declare that a custom race will be treated by the game as one of the standard races

if you use SetRaceAlias Customrace Dunmer then anyone of the Customrace will have GetIsRace Dunmer return true, so scripts, dialog conditions etc will work, in vanilla or mod-added code.

I don't recall anything In Wrye Bash doing it externally. That function would have to be called in a quest script each time the game is loaded.