You'll only get stopped if it is extremely loud, most Arrow's systems i've heard on RS's were never that loud until the powerband kicked in.
You might also want to check if the 3 bolts have the same positions on each can, if not you'll have to not be lazy and take the fairing off and swap the whole system. Which isn't hard at all.
I know Arrow made a bolt on can to go straight on the original 'prila expansion chamber, but i'm not sure if the full system as the same can. More than likely does, but you never know. It's worth checking out, and it's only a few bolts.
On some race cans it will have stamped on it somewhere 'not for road use', if you do get stopped and they see that, i'd imagine you'll get a slapped wrist if you're lucky, points if you're not so lucky. Not 100% sure on that though.
If you do keep it on, just don't ride like a twat and you should be fine.