Crash course, how does this work again?
Is it, "look, if I screw this NR barrel on it, it then an NR rifle, so it doesn't matter if I swap out the barrel to an R barrel, because if I put the NR barrel on it, it's all good"?
If that is the case, do you need to carry your NR barrel with you at all times? I can't see an officer being happy with that sort of logic if the NR wasn't around. Heck, I can't see and officer being happy with that sort of logic even if the NR barrel was around.
It doesn't work and is illegal.