1.. Make sure these servers are in 1 group.
2. Create distribution for SEPM would be your normal Distribution
Give LUA info in SEPM in SEPM -Admin- Servers- Local Site- Properties- Liveupdate- Source Servers.
3. Create a new Distribution and in this distribution first you will test it..once it has been tested it will be published only to Critical App group.
for that you will have to create a new Liveupdate policy
uncheck -default management server, check the second option for symantec liveupdate servs then add the LUA clu-prod link below.
So here..SEPM will get defs from LUA and it will distribute to 1950 clients in one go..
The 50 servers will not take defs from SEPM they will directly connect to LUA distribution link to get the updates once they are tested.