You can either drag and drop the clients from the servers in the old groups onto the desired server in the new group or you can copy the GRC.DAT and PKI\root certificate files to all the clients. The stations periodically check for the GRC.DAT in the correct folder and read it in if it exists. For example, I put the following two lines into a startup script in a group policy to push out the GRC.DAT and certificates to all my 10.x stations.
COPY \\SERVERNAME\VPLOGON\GRC.DAT "%ALLUSERSPROFILE%\Application Data\Symantec\Symantec AntiVirus Corporate Edition\7.5"
COPY \\SERVERNAME\VPHOME\pki\roots\*.* "C:\Program Files\Symantec AntiVirus\pki\roots"
Those examples use 10.x destinations. The GRC.DAT destination path may vary slightly if you're reconfiguring older clients (i.e. 7.6, 8.0, 9.0). The second line is not necessary for the older clients, just 10.x clients.