Still not quite buying it. I can access the handle, owner ID, and other read-only properties on :vlr-Modified reactors. The block reference object itself is the first argument of the callback function. THe attribute being modified is passed as an entity (yah, not a vla-object) in the params_list and even then, trying to work back up through the owner ID still fails. I can process *that* to my hearts content, but I really need that owning block reference handle/ID. There's no command involved to hook for a post-process function, either.
I'll just have to replace the :vlr-subObjModified on the block reference with a :vlr-Modified for each of the attribute references. PITA, since I have to process the OwnerID to the get the owning block reference, but at least it works.