Hi,
As above stated it's not possible to merge to SEPM's with each other.
If you wish to remove one SEPM, you can migrate all load to single server.
If you wish to use both SEPM's , replication/ Failover & loadbalancing can be one of the available options.
How to install the Symantec Endpoint Protection Manager(s) for replication
http://www.symantec.com/docs/TECH105928
About failover and load balancing
http://www.symantec.com/business/support/index?page=content&id=HOWTO26809
About load balancing and roaming in Symantec Endpoint Protection 11.0.
http://www.symantec.com/docs/TECH104519