In my system some alts insisted on being called their own name, and some refused to associate any name with themselves at all. Some answered to the birth name for the sake of convenience, although there has been no part of us here that has associated their sense of self with the birth name for as long as I can remember.
I have not legally changed my name, but I - as a mostly integrated self - am known by a different name and have been so for many years now.