Changing the regulator will require a reflash, but I don't think you need to do this to change the pump. As long as the new pump has equal or greater flow characteristics, it will work the same as the old one. It might be louder or less efficient, but unless the fuel lines (particularly the return line) are so small that the regulator can't bypass enough fuel to keep the pressure delta at 4 bar, a stronger pump won't be a problem. And in that case you would just run rich, which is by far the less severe error.
That being said, I don't think the cost savings are worth it, unless you are looking for a science project.