The bottle shouldn't have flown around the room if the burst disk went. The BD nut should have 2 holes in the sides of the nut so the escaping co2 vents in opposite directions so the bottle stays put. Pre 2000 PMI made some co2 bottle valves with burst disk nuts without the holes, they are currently offering a reward for the return of these! (I'm pretty sure this is PMI USA not PMI Europe).
But in answer to your question, no you shouldnt take a burst disk out of one valve and put it in another. Once it has been torqued it shouldn't be loosened and torqued again. I've no idea if the 12oz takes the same burst disk as the 20oz btw..
If your burst disk is just a disk on it's own, Powerball in Aldershot will sell you another, or better still, replace it for you if you don't have a torque wrench, If it's the sealed unit type (disk is sealed onto the nut) then i know PMI in Dartford do these. In either case it won't cost more than a quid.