I doubt that will be restricted to armorer. One, the armorer is never going to have the correct module, so people are going to buy their own, and two there is almost no way you can stop people from changing. Yes, if you have 200,000 pistols something like that is an issue.
From what I've read for the M17 the plan is for the module swap to involve a separate step from that of the civilian and law enforcement P320. I believe this was a request of the Army. If I get the time I'll try to find some pictures that I think show this. I've actually gotten to look at a real M17 at the SIG Academy Pro Shop, but I'm pretty sure they're not going to let me pull out the FCU on it.