Its not normally just a cut, the OEM parts with visible exhausts have a plastic moulding that goes back 2-3 inch's providing a cup around the top of the pipes, might look ok just cut out but might look a little bit un-finished. Suppose it depends on how much you want to spend, you can always get the new bumper after they have cut (as long as they exit the pipes in the same position)
Can you not just get a 170TDI back box and fit that?