Hi,
Those certiricates between HPDM Server and MRC are not designed of customizable. Please submite an impact case if you have any security concern on this.
Just FYI:
hpdmcert.key is for communication between HPDM Server and HPDM Gateway
hpdmskey.keystore is for the communication between HPDM Server and MRC
server_keystore is for the commhucation between HPDM Server and HPDM Console