Better sights make a gun safer to shoot, better triggers make the gun easier to shoot....Whats the difference between adding sights and adding a different trigger. Id like to see someone post 1 case of self defense that was lost solely because the person had put an aftermarket trigger in their pistol.
I don't know if its fair to ask a common person to prove a court case exists, when most people don't have access to the thousands of self defense court cases and where to find them. But its not unreasonable to say the subject wont be used against you in court such as Santibanes v. Tomball, TX. I think the general idea is a custom trigger is fine as long as it doesnt lighten the trigger pull from the factory trigger.
The consideration to take here is the advice from lawyers and reputable trainers who will never suggest to lighten a trigger.
Heres a good reference from a legal expert on the subject,, including referencing cases where trigger pull was brought up in court.
Gun Modifications
armedcitizensnetwork.org