Make the Berretta Pistol's Magazine Release left handed:

 

First make sure that there is a slot on both sides of the magazine for the magazine catch to lock into.

The parts of the magazine catch assembly are 20, 21, 22, 23. 23 is a spring which powers everything. 21 pushes against the button end of the mag catch body (20). Part 22 pushes against the body of the pistol forcing everything toward the button end. With something like a dental pick, push part 22 toward the button end. when it clears the frame draw it to the rear releasing it. Remove parts 21,22,23 into the magazine well. Draw part 20 out to the side. Reverse part 20 and re-insert it into the frame. Reverse parts 21,22,23 and reinstall them. Your mag catch should now be left handed.

It's not an intricate job but it does take some finesse.