I have the same question...
I want to Auto Exclude new components from all the existing Simp Reps except for the one I have active.
I heard a rumor that this is possible but I haven't found the details yet.
I don't see the answer in this topic...
You have options when you create a simplified rep.
1. Set the top assembly to exclude and nothing new is added to the rep unless you add it.
2. Set the top assembly to master and everything you add is in the rep unless you remove them.