I would not be surprised if she changed her legal name, but she would be stupid to change her professional name since she has established herself as Katy Perry.
For the record, her legal name isn't Katy Perry anyways, it's Katy Hudson. She goes by Katy Perry because she didn't want people to confuse her with Kate Hudson.
Of course. It's pretty standard. just like hannah montana/miley
Can't have people finding out that hannah montana is miley