You could try sending an e-mail... Btw, have you checked whether the username "Hamster" is available on the forum? If it is, you could create a user with that name, and use that one instead. Even though your old posts will still show up under the username Uh_Mari_Ollis, you're new on the forum and haven't written so many posts yet.
NeutronStar could do the same with Atomic7732 (I guess he already has an account with that name on the forum), but he has also written many posts on the forum.