If I'm wrong on this don't abuse me too much.  

Can I run a RRA PDS (or any other bufferless 5.56 system) on a lower with a buffer set up for 9mm?
My thought is to facilate caliber changes without too much of a compromise in function and reliably if any.
I really want do to this type of a setup so I can shoot any of my base ammo .22, 5.56, & 9mm.

A sidebar question; Can I move a .22 conversion for an AR around from gun to gun or do they brake in to the unit that they were originally run in, and run the risk of damage if moved?

Thanks

9mm buffer will work just fine in a 5.56 rifle*.  Lots of people running their guns that way.  That said, I believe RRA has warned against trying to use their PDS uppers on standard lowers, something about the BCG smacking into the back of the receiver if you do.
*(unless you're running one of the extended 9mm buffers.)