You need to do this in the User preset area, not in a setlist. When done within a setlist it simply creates a copy of the original, with the same name, on the assumption that you plan to use the same preset at different points during the set. If you want to use a new preset in that particular Setlist slot you need to create the new preset in the User preset area, use the Save As operation to rename it, and then assign it to the Setlist slot.