We ask all resellers not to use the the features in WebHost Manager panel for changing an account username or domain. These features contain bugs and will break the account in question in several areas.
An account username is only seen by the account owner (not regular web visitors to the site) so there is no reason this should be changed. However, if it really does need to be changed (or the domain name) then we ask that a new account is setup in WebHost Manager with the new details (desired username/domain) and the files manually copied across by downloading via FTP from the old account then uploading to the new one.
Settings such as email accounts, databases, etc should all be setup again in the control panel for the new account.
In some cases a reseller may need to change their main domain (and private nameservers where applicable) on an already active account. Again, we recommend against this for the reasons set out above but in cases where it really needs doing we can take care of it but have a £20.00 + VAT one off fee for doing so due to all the manual work required on our part.