Following a self-defense shooting, there's a fair chance that the shooter will be sued by the bad guy. A homicidal/suicidal armed robber took three gun store employees hostage here in the SF Bay Area about 10 years ago; one of the gun store employees shot the robber, who survived. The robber filed a civil suit against the gun store and the employee claiming that he was shot negligently. The suit was settled with a minimal payment to the robber from the store's insurance carrier.
My point in mentioning that is not to inflame everyone with the idiocy of it but to point out that the legal theory underlying the alleged liability wasn't that the employee chose to commit an intentional tort - but that he was negligent, and that his negligence caused an injury to the plaintiff.
In that context, something like a trigger modification or home reloaded ammo would give the potential plaintiff more points to argue. They don't have to argue about whether or not the defender was in fear of his life, they can argue about whether or not his finger slipped, or whether or not the gun fired itself, or other ridiculous things.
The "how are they gonna catch me??" ideas go nowhere, legally speaking. If you "lose" or modify the gun after the shooting, you're giving the plaintiff a chance to argue that you did so to destroy otherwise admissible evidence. If a judge buys that idea, he can instruct the jury that they can (or even must) assume that the evidence that's not available would have been favorable to the plaintiff (bad guy) and unfavorable to the defendant (self-defense guy).
Civil suits include a process called "discovery", where each side must disclose essentially everything it knows about the underlying dispute to the other side. The precise details of this depend on the court you're in, but the underlying idea is the same. The other side can force you to testify, under oath, about how and where you bought the gun, the ammo, the holster, and how they were modified, if at all. They can force you to turn over any records you have that will show those things. Compliance with this is somewhat self-enforcing - but if you're caught fudging the evidence, it's likely to turn out very badly for you.
Remember the lesson of Watergate, Iran/Contra, and Monica Lewinsky - it's not the crime, it's the cover-up that gets you.
And yes, if you're potentially talking about a verdict or settlement in the hundreds of thousands or millions of dollars, someone will take the time to take your gun apart and figure out whether or not it was factory stock or modified or badly maintained or whatever. There's plenty of disagreement among "gun people" about what's safe and what's not safe - and all the plaintiff needs to do is find some gunsmith who doesn't like whatever it was that was done to your pistol, and ask him to testify that the mods made it possible that for some reason the shoot was the result of negligence, not an intentional act.
(But, having said that, I also want to say that I think these "bad guy sues defender" lawsuits are mostly urban legend; and that many states have reasonable "castle doctrine" or other rules that help defenders. I don't think people should organize their lives around the tiny possibility that they might be involved in a self-defense shooting, and that that shooting might lead to a significant civil suit. It's possible, yes. Buy if you're not an LEO and you really believe that there's a good chance you're going to need to shoot someone in self-defense, you really ought to worry about changing the rest of your life to reduce your risks, instead of worrying about parts in your carry gun.)
Notice the red hue...
