My guess is that if you try to do it before the flight is cancelled, you will be referred to QR (and QR is most likely uninterested in any AY-introduced waivers and will look at award availability only). But if you wait until the flight is actually cancelled and AY sends you both the cancellation notice as well as the rebooked itinerary, you then have the option of changing that itinerary online at AY MMB, including for flights the next day.