Instead of trying to change the liveupdate policy to use a specified internal iveupdate server you are going to need to edit the management server list to point these remote 200 clients to the other server. In policies just under liveupdate expand policy components then edit manaement server lists, add a list then add this new SEPM as priority 1 and assign it to the group you have these 200 machines in.
After doing this, change your liveupdate policy back to use default management server as the clients will be pulling defs from the SEPM they are checking into (your new server).