Hello,
It is not possible. you need to install SEPM 2 as additional site.
How to install the Symantec Endpoint Protection Manager(s) for replication
http://www.symantec.com/docs/TECH105928
Also, check this Article:
https://www-secure.symantec.com/connect/articles/replication-and-considerations
Have you already started Deploying of clients on SEPM 2?
If yes, you can then -
1) Use the SylinkReplacer Utility to get those client communicate to SEPM 1.
2) Once all the clients communicate to the SEPM 1, you can later Uninstall SEPM 2.
3) Reinstall the SEPM 2 as Additional site and get back those clients reporting to SEPM 2.
Hope that helps!!