Run SepMasterService as domain user

How can the SepMasterService be configured to run as a domain user instead of the local system account?  This is for EMC CAVA and the client version is 12.1.6.  I've tried disabling the tamper protection and changed the client control setting.  The settings for the service continue to be greyed out.  Logged in with different accounts that have local administrative rights.  Any help is appreciated!