I more or less did this... couple semesters into a CS degree I did a 180 and got into my colleges art program. While I had a blast I still don't think it left me in a position where I could get a gig as a full time UI/Graphic Design guy. Like anything else, you get out what you put in and I spent too much time coding outside of class to ever get real good at the design. Still happy I did it though because I am at least able to scrap something together when I need to.

TL/DR: Studying something in college != being a pro at it