So if I have a subassembly that needs to match up to a larger assembly, I make the subassembly flexible, and match up to the parent assembly within the parent assembly's document. how do I then make the subassembly's saved rigid state refelect the geometry it has in the parent assembly?

I haven't gotten into much top-down design, so I am not sure where to go on this one other than manually adding distance/angle relations, but that would over define the subassembly in the parent assembly the moment anything changed, so it's probably not the best answer,