Parenting can't be switched.  If your problem is getting the second instance to line up with the first, make it from the first.

Save the materials of the first, and at the point where you would switch between the two export the prop to OBJ.  Reimport that prop, unchecking all import options.  It will land right where the other was, and that will be the second instance.  Apply the materials to it.

If I misunderstood, just ignore me ;)

John