You asked it differently before, I would say, but that's fine.
The evaluation of changed product rule means that every area of change would have to be evaluated for the impact at the product level. When people talk about certifying the whole aircraft, in essence, those 1,200 requirements have to be looked at and a decision made about the extent of the change—38%, different engines, different performance—and the airframer has to reconfirm compliance with the requirements.