Not yet, but according to this article you will be able to soon:
link
"-User name changing. Yes, apparently, a few people want this for some unknown reason. What the heck is wrong with bonerAlert89 ? Gold will keep this from going too crazy as it's hard enough to keep up with your 1,000 fans and all their new names each week."
Basically, they're soon adding a feature where you can earn "gold" for doing certain things on Fanpop, and one of the many things you can spend it on is changing your username. The fact that you will have to spend gold on it will mean that - hopefully - users won't just be mindlessly changing their username every few minutes. They will have to think carefully about it first.
