Originally Posted by
FlightDetent
Not that the N1 limit is any different for the two, actually.
It is an EPR limit not a N1 limit. As both engines are still operating, autothrust is still active while in one is CLB and the other in IDLE. Autothrust would deliver up to the EPR limit value associated with the CLB thrust rating mode to maintain the speed target. As you suggested at that sort of cruise level a change of thrust rating mode from CLB to MCT or even TOGA would not change the EPR limit value.