Is it possible to change the hostname of my Enterprise or Domain Manager
No. Any change to the hostname of a Manager, even to the FQDN will break the ITCM infrastructure and cause massive and unpredictable problems.
CA support will not be able to assist in working arround this. If you have renamed your Managers the only option is to revert the servers to their original name and even after this you may need to restore from a good backup.