Re: RG320FM.. Edge 3 to Lo-pro Upgrade
No, replacing the Edge III with an Edge Pro or Lo-Pro will need routing. The only swap that (allegedly) doesn't need routing is Edge III to OFR. Even with that swap the OFR may have a different string radius. The only trem that easily swaps with a Lo-Pro is the Edge (also an amazing trem, so most people wouldn't swap it) and the Edge Pro II swaps with the Edge Pro.
Back to the point, you'll need routing. I suggest buying a Lo-Pro. It's low-profile, fine-tuners out of the way, amazing tuning stability, and looks smooth. The Edge Pro is all of these things (with smoother looks) IF it has the locking studs. If you're buying an Edge Pro, get the locking stud mod from Rich.
So Lo-Pro (amazing)
Edge Pro (amazing with studs)
Either way it's a win-win; you will need routing though for both.