I don't know. If it's a door or window and especially if you have multiple doors and windows, it would be easier to do a perform by selecting the subprop I would think. If it was all lumped under the main prop then it would become a long list and you would have to try to distinguish between the various subprops. For one of my recent movies, I created a mixing console with the controls and switches animatable and all being subprops. I did set the pivot point for each control and switch, but it did seem to work correctly that way. I didn't try a merge, so that may well not work correctly.