I buy the best defensive weapon I can afford, equipped with the best sights, stocks, and of course the best feel. If asked why I can/will tell my attorney, I buy the safest car possible why not buy the best weapon possible. I don’t modify my cars(anymore) and have no reason to alter my weapons. I am not a gunsmith.
I don’t care if you change your stocks or your sights, if it makes the weapon safer for you, great. I do remember a story of some police officers changing the trigger pull weight on their service weapon. The jury found them guilty, based on the modification which in their mind allowed the trigger to be pulled too easily.
If you buy a weapon that does not measure up to your needs, sell it, buy another, but in my view I suggest, when possible, rent a weapon and try it. The selection of a weapon should be taken with great care, your life may depend on it.