I, also, have heard the same thing about not modifying your carry weapon. The other thing I've heard is to find out what ammunition your local police are using and use the same, identical ammo. That way, if a lawyer suggests that you built and load a weapon just looking for the opportunity to kill someone, your lawyer can say that the gun is non-modified, just like any weapon on the shelf of your local gun store and the local police use the same ammunition that you are using.
Apparently, that can make a difference if you ever have to go to court to justify defending yourself or someone else.
In classes I took, years ago, I was taught to yell "STOP!!!" before shooting so that if there are any witnesses, they can testify that the shooter told the bad guy to stop "before" actually shooting. That is supposed to look/sound good in a courtroom.
When I took classes, I used a S&W, Mod. 66, 4" barrel and shot .38 wad cutter's for paper targets. We absolutely could not pull the hammer back before pulling the trigger. At first, I thought I would not be able to hit the broad side of a barn but, with practice, it became very comfortable and accurate.
I shot thousands of rounds using that technique with no problems. I used to buy reloads for the classes in boxes of 1000 & I bought many boxes. I loved that S&W-66. It's a great gun and extremely reliable, however, a little old fashioned by today's standards.
Joe