With enough money, all (or almost all) things are possible. But most pistols that use a decocker are not designed to be carried cocked and locked, so the decocker would have to be altered, or a separate safety would have to be designed, made, installed, and fitted. I think I can pretty well say that even if it could be done, it would not be worth it. Buying a gun like the CZ-75 would make more sense.
Another factor is that if a gunsmith did alter the action in that manner, and the gun owner shot his toes off, it is a good bet that he would blame, and sue, the pistolsmith who did what he was asked to do.
Reducing pull weight and smooting actions are the bread and butter of pistol smithing and can be done by almost any competent pistol smith (although the breed is becoming rare today).
Jim