no, i dont think you can change it...but, you can sign up again but you will lose all your post count. also, you can (if you sign up again) can tell every one that you ust to be an old member (dolphen)
PM Admin; he may be able to change it for you. But try not to pester him about it often...Choose a name you will like for a long time. I imagine that Admin is busy and doesn't have the time to always keep track of changing people's names and such.