cPanel VPS administrators take note...

Changing your servers hostname WILL invalidate your cPanel license! (The hostname will also change back to what Spry set it to on next reboot anyway, so don't change the hostname yourself.)

If you want to change your servers hostname, create a ticket for our support technicians.

If for some reason you still want to change your hostname without making it permanent, and need to access WHM/cPanel, either reboot your VPS to reset the hostname, or SSH to the server (as the root user) and run /usr/local/cpanel/cpkeyclt. This will update the license file with your current hostname, and push the change to cPanel's license verification servers auth.cpanel.net and verify.cpanel.net.

More info at cPanelPlanet.com