remove ldap login name from guest account/user

Hi,

I've merged an user with the 'guest' user by mistake. The original user had a ldap-login name which is now linked with the 'guest' account, so if I lock the guest-account the original user can not log in any more. Is there a way to delete the linked ldap-login information from an account? Or is it possible to delete/reset the guest account (as renaming and deleting of the 'guest' account is prohibited)

thanks in advance