This is a subject that has been discussed may times and the answer is it could. In a SD scenario, after the shooting comes the shooting investigation. The investigation will determine if you were justified in using deadly force or not. The investigators will look at your gun and ask you routine questions about it. After the investigation your case is presented to the Grand Jury for review. The outcome of that will be indictment/no bill. Indictment=go to trial, be acquitted or go to prision. No bill=go home. Whether you are indicted or no billed, tried or acquitted, there will ALWAYS be a civil trial. You can take that to the bank. During this civil trial is where mods to a gun will come into play. Anything you do to a gun that deviates from factory specs will come into question. Things like lighter triggers, polishing/honing of internal parts, removal/modification of factory installed safeties. Even something as mundane as adding night sights, a tactical light or even a magwell will be questioned by the plaintiffs. How do I know these things? I've been there and I'm in the middle of a civil case now regarding my last on-duty shooting. The gun I used was a slightly modified 4006TSW. By slightly modified I mean I added night sights, a light, had the feed ramp and breechface polished and added a lighter hammer spring . All this was done by S&W at my request. Everything I mentioned above has been brought into question by the plaintiff's attorney to make it sound like I did these things because I wanted to kill the deceased when in fact everything I had done was to make the gun more reliable/user friendly. I was questioned about every single thing done to the gun. Here are some of my replies:
Night sights: To ensure I hit what I'm aiming at and not injure or kill an uninvolved person by a poorly placed shot.
Tactical light: So I can identify my target and backstop.
Polishing: To enhance reliability
Lighter hammer spring: Because I didn't like the double action trigger pull.
So, with all that being said modifying your gun MAY be an issue if you're sued. The kicker is this, as long as the mods you make don't void the manufacturers warranty and do not make the gun inherently unsafe you'll be fine.