As far as I know there is a way to change usernames on the forums but as far as I'm aware Badspot (or any of the other forum administrators) have never actually done it before. You'd have to rely on an admin doing it for you, though. You'd have to have a seriously convincing reason as to why they should go through the effort. You can try to ask, but be ready for disappointment.
Is having your new name on the forums that important to you? Do you intend to buy another key for a new account if that's the case? If so, I recommend that you put a link to your new profile on your old one when you register the new account. You don't have to, but I recommend doing this in case people ever try looking at your old profile.
Either way, best of luck to you.