There is nothing to stop an obj from having extra parts - I do this all the time. The problem is happening when you try to load BOTH cr2's that reference the same obj. Why do that? Why not just have one CR2 that contains everything you need in version 1. Then when you upgrade, tell user to stop using that CR2, and use your new CR2 - which again contains everything it needs. That is, The new CR2 would go ahead and reference all 6 parts, so that you no longer need to load the old CR2.