In case someone might stumble on this, the learning process goes on...
It's very easy to "isolate" one or more components
in an assemble using the View Manager and Simp Reps.
Simply start the View Manager / Simp Rep and switch
to the Properties view. Assuming you've started with a
clean rep, the top level component will already
be listed. Select the components you want to isolate
in the graphics window (or Model or Layer Tree) and
click the Master Representation button. This will add
them to the list and Exclude the top level.
Switch back to the List view and create a new rep if you
want to save the state (and were working in Master Rep
or want to preserve any other rep you might have started