Changing out grips and sights should not be an issue as even some federal agencies allow those modifications to duty issued/authorized handguns. I don't think that aftermarket recoil springs/guide rods/ recoil reducers would make any kind of ripple. Trigger modifications that reduce trigger pull weights seem to be the issues that will get someone in trouble, especially if the shooter or his/her attorney cannot reasonably articulate why the modification was performed and why it did not have an adverse effect on an otherwise justifiable use of deadly force. I don't know that you'd have any problems if a qualified armorer smooth and polish the mating surfaces in the action (removing burrs, etc) simply to smooth out the trigger, but modifications that create a "hair trigger" should be avoided for a self defense pistol in this day and age. Not sure that some of those modifications over the years were even all that smart back when one could get away with it. There was a time when law enforcement training recommended prepping the trigger as soon as the pistol was out of the holster. That was when DA revolvers were the rule and not the exception (And there was a run of Colt Troopers with 20 lb DA pulls). I still hear it and read it from time to time from trainers here and there. Being used to a heavier trigger pull and then switching to a handgun with a light trigger while under stress can lead to a premature discharge if you are prepping the trigger during presentation. Even going from a standard Glock or S&W M&P trigger pull to something lighter can be a problem. As others have suggested, Google Massad Ayoob's publications on light triggers and court cases involving use of handguns for self defense.