One client asked for his account primary domain name in WHM to be changed, to solve that I entered the WHM admin and navigated to:
Main >> Account Functions >> Modify an Account
A plenty of options concerning the user registration are available for changing from WHM’s Modify an Account, the only one I had to change was under the field Primary Domain e.g.:
Primary Domain: server-domain-name.com
Chainging it to let’s say new-server-domain-name.com and Saving the settings changes the primary domain for the user.
Bear in mind that if the user has already tried to modify his primary domain himself changing the list of his addon domains the above decribed procedure won’t work out because of a WHM Cpanel admin bug.
If this happens a shitty error msg Unable to change domain name will appear and the Save button on Modify Account will not work out.
The only resolution to this I’m aware of is to completely delete the problematic user account and add it to Cpanel again.