Oh, I get it now.
So, you have not decommissioned your old server.
Basically, right now, you have 2 servers running simultaneously.
Server 1 (old) and Server 2 (new).
You did not import the database into server 2, but rather only the certificate from server 1 in order to re-establish communications from your 500 clients to the new server.
You than created a management server list, which contains both the new server and the old server in the old servers management list.
Your clients have received the new management server list and can now "theoretically" communicate with both servers.
Your question than becomes, what's next for the clients to ditch the old server and move over to the new one - the catch, without using replication to avoid carrying over settings you don't want anymore.
* * * * * * *
1 - Create a new group (migration for arguments sake) on the old server.
2 - Create the same group (migration for arguments sake) on the new server.
3 - Place a few clients in that group.
4 - Change the management server list priority for the newly created group on the old server, and place the new server as the primary server for communication.
What should happen next, is the clients, being told to move servers should ditch the old server and move to the new one...