Hi dufer, It should be possible by modifying the AccountID directly in the database in the [Accounts] table. Please check also, if there aren't any records in the [AccountRights] table for specified AccountID and if so, please modify it. I tried it on my testing environment and haven't found any issue (account limitations are kept, discovery profiles created by the old profile are working).
Please let know if it helped.
Found a much easier way. Simply change the name using "Manage Accounts".