I doubt the barrel is 'user changeable' anyway... and Ian would likely need to use some of the parts from the original barrel on the NR barrel. But I'm sure he'd give you the chunk of rifled steel back if you wanted it.
I think an NR SAF would be pretty sweet.. .but you'd need a pretty big barrel shroud to make it look like a supressor, otherwise it'd look pretty stupid (IMHO). What's the stock barrel length on the SAF as it stands now?