Thanks for asking this question before taking a shot in the dark! Changing the hostname of a Katello installation is pretty serious business since we have strict usage of SSL across all components, and down through the registered Content Hosts.
A utility called katello-change-hostname is installed on every Katello server and provides the functionality you’re looking for. Be aware that performing this change requires that clients are re-registered after installing the new katello-ca-consumer RPM after the hostname-change utility completes. Be sure to take a backup due to the impact of this change.
Unfortunately the utility is lacking true documentation, but typing katello-change-hostname -h will show how can you invoke it.
Would be nice if you can add custom values as in my case I dont want puppet installed. (I now I can just rerun foreman-installer but now I have additional work to fix my puppet agent running on the machine)