I'm afraid it's no simple matter. As these are 2 separate and independent SEPM sites, in order to combine them both into a Single SEPM farm, the DB on one of the will be lost. In terms of a project to allow centralised management of both envorinments, I'd recommend the below steps:
- Pick a Primary SEPM (either one will do, but I'd personally pick the one that manages the most clients, call it SEPM2)
- Setup a brand new SEPM in the smaller office as a replication partner to the Primary SEPM (let's call this new one SEPM1B)
- Recreate groups and policies in the new SEPM farm to mirror the settings from the smaller site's original SEPM (SEPM1)
- Move clients from smaller site's original SEPM to the new replciation partner SEPM on the same office (SEPM1 -> SEPM1B)
The reason for this is that setting up replication requires mirroring a DB from one SEPM to another, which means wiping out the destination SEPM's database (losing all config).
Doing it the way I've described above, means you will arrive at a stage where you have the new SEPM (SEPM1B) ready to go, and can migrate clients across to it in a controlled and staged manner, as well as leaving the old SEPM (SEPM1) handy in case you need to move back.
The intricacies of the above con be found in the below articles:
Replication:
http://www.symantec.com/docs/TECH93107
http://www.symantec.com/docs/TECH105928
http://www.symantec.com/docs/TECH91509
http://www.symantec.com/docs/HOWTO81029
http://www.symantec.com/docs/TECH95122 (just in case the DB is huge)
Move clients from one SEPM to another (Step 4):
http://www.symantec.com/docs/HOWTO81116 (you need the MSL from SEPM2B)
http://www.symantec.com/docs/HOWTO81111
http://www.symantec.com/docs/HOWTO80762
http://www.symantec.com/docs/HOWTO81109
http://www.symantec.com/docs/HOWTO81179
https://www.symantec.com/connect/forums/how-change-sylink-client-using-snac-1215
https://www.symantec.com/connect/forums/need-make-unmanaged-client-managed-client-must-be-done-remotely
https://www.symantec.com/connect/forums/sep-1107-sepm-1212-communication-update-package-fails
In terms of licensing, the SEPM farm (SEPM2 and SEPM1B) should have both licenses installed on it (licenses are automatically replcaited across both so you only need to do this on one). The licenses on SEPM1 can be left where they are. As long as the total number of endpoints does not exceed the total number of endpoint licenses, you should be fine from a license perspective.
Alternatively, you can get in touch with a Symantec partner (like ourselves) for PS to perform this sort of migration for your customer.