patsfan:
If the smith has experience doing it, it's about a half-hour of bench time. Something like $50, I suppose. Probably a bit more if he's not tried it.
You can DIY the whole project, but swapping the sear spring has to be done in a plastic bag 'cause parts
will go flying.
Taking the rear sight off the Shield is supposed to be a real bear, too. I think they're using the elephant that Kimber uses to place their rear sights.... A good smith should have the skills, and/or a pusher, although a lot of cursing and some luck (and a nylon or brass punch) helps a lot.
I'm not a lawyer, but my guess would be that
selling (at an FFL) the gun might be a problem. Owning it shouldn't be. It's just a spring swap, and a "what the heck - it's always felt like 5#" defense probably would fly. S&W is stamping those out fast enough to assume somebody'd put the "wrong" spring in there....
It's NOT a "shoot it until it smooths out" issue - I don't think you'd lose more than a pound, if that much, if you bought Winchester and devoted your life to WWB's

.... Unless the spring breaks.... Shooting it WILL clean up the drop safety, trigger bar, and sear interfaces a bit v.s. just some polishing, but the full Apex (or Burwell) treatment of the drop safety may be better. Heck of a lot quicker, too

....
Regards,