Depends how big system it is. If really big one you can do part by part. One more point is what is the header & branch size. Say header is 24 " & branches 4". System can be break. At all branched interface point feed displacement data from header stress calculation report along with SIF at that point.
If there is no much difference between header size & branch size then you can not break the system at header branch interface, you have to find some other suitable point at branches to put anchor & isolate systems.