People generally fall into two camps. Those who reject any answer more complicated than "Do" or "Don't" and those who understand that sometimes simple questions have complicated answers.
If you're one of the people who believe that questions must have simple answers, then the most accurate answer is "Don't".
If you're willing to accept a more complicated answer, then the answer is: "It depends."
It depends on a number of things:
1. How it was modified? Does the modification smooth the trigger? Make it heavier? Make the pull shorter? Does it disable or alter the function of any of the safeties of the pistol? Some modifications are pretty bulletproof. Others could open a can of worms.
2. What was it like initially? If the pull was unusually heavy for a firearm of that type, then having it changed to meet the typical spec is likely pretty safe. If it was already typical, then it may be necessary to explain how the modification really made it better. The explanation will need to be so simple that someone who's not interested in firearms can easily understand it.
3. How did it end up/how does it compare to the triggers on other similar pistols intended for LE or self-defense use? Pretty self-explanatory. If it's obviously atypical for a self-defense/LE pistol of its general type, then one should be prepared to justify the difference. Some results might be easy to justify, others could be very difficult, or perhaps impossible to justify.
4. Who did the modification? If you sent it back to the manufacturer to remedy an unusually heavy pull, or to remedy some other problem, then it's obviously going to be harder for someone to argue that the change was performed improperly or that it resulted in an unsafe configuration. If you bought a part off the internet and put it in yourself, that might not sound nearly as safe or proper to a jury. Expect to have to provide a good explanation--or to pay an expert witness to do it for you.
5. What were the other circumstances of the shooting? It is possible for the circumstances of the shooting to be so blatantly obviously justified that no one is ever going to question anything about the gun. If you happen to be on the scene when a mass murderer slaughters the security detail and tries to shoot a supreme court justice during a live tv interview and you stop him with your carry gun, it's pretty unlikely that there will be any questions about what kind of gun you used or how it had been modified. On the other hand, if the circumstances of the shooting are such that there's some room for doubt about its justification, then one could reasonably expect that issues that might otherwise be glossed over might get a center stage treatment.
Things to keep in mind:
1. If firearm modifications become a topic during a trial, no one is going to care much about your opinions on what's safe or reasonable when it comes to firearm triggers. That will be decided by expert witnesses, manufacturer recommendations, etc.
2. Your fate will be decided by a bunch of people who learned about firearms from watching movies and tv shows. You won't be arguing your case against a bunch of gun enthusiasts.
3. You'll be arguing against a person whose profession is making people look guilty and that person will be performing for the benefit of people who have never sat in your position and don't have your knowledge of firearms.
4. It's important not to focus exclusively on criminal prosecution. Civil prosecution may not take your freedom away, but it can take virtually everything else away from you. It's also much harder to defend against a civil suit since the standard of proof is much easier.
5. If the modification makes it easier to argue that your self-defense shooting was more likely to be an accidental shooting than an intentional one, this could be a very attractive option for the basis of a civil suit. Depending on the circumstances, an accidental shooting may bring your insurance company and their deep pockets into the suit as a defendant alongside you. Insurance companies pay for accidents--but usually not for intentional acts.
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Bonus material:
Bob: Let's say I am attacked by three persons acting irrationally. One large and strong unarmed person with a bad limp, one very small person with poor eyesight confined to a wheelchair and armed with a firearm and one medium-sized person with a baseball bat and a prosthetic leg. So since I'm carrying my super-modified race gun with the 1lb trigger, I shoot the glasses off the guy in the wheelchair so he can't see at all. The guy with the baseball bat trips on the glasses and falls down. Now, if the large unarmed guy with the bad limp comes at me slowly, would I be justified in shooting him too if my only avenue of escape is to cross a road with a medium level of traffic which could endanger my life?
Bill: Wait, you're using a gun with a modified trigger for self-defense? Don't you know that experts say that could cause problems in court?
Bob: Yeah, but I don't care--why should I waste my time worrying about something hypothetical like that!
