cPanel 11 WHM will most likely solve all these errors, however, if you still facing problem, try the following steps to change hostname properly:
Login to server via SSH as root.
Run the following command to change host name: hostname servername.domain.com
Change servername.domain.com to a hostname you desired based on your domain name.
Run the following command to update cPanel license information to avoid invalid cPanel license error: /usr/local/cpanel/cpkeyclt
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