@delaiah You can use parts from different kits together in the same instance. Load up two AR Modern Drummer nki's and mute the parts from each kit you don't want. But that'll obviously compound your other gripe, loading time. You could how ever save it as a multi (.nkm) to avoid having to load up two full instances. It would just load up with the parts you wanted.
good idea, but sounds like a huge pain in the rear to accomplish something that can be done with other instruments easily. also, you'd need to make many of the adjustments twice and last but not least, the room mics likely had different settings for the kits, so they might not match.