I've often wondered the same thing. I have an example that worked even though the data point is with IHG and Mr Rebates. I had a 3 night reservation for a hotel at 10% cash back. Since the cash back dropped to 5% I decided not to cancel. Instead, I modified it to 4 nights. A few days later, I modified it again for a second room. I was expecting to either get 3 nights for 1 reservation or 4 nights for 2 reservations, or the most likely outcome, zero cash back. Oddly enough, I got cash back on 4 nights in 1 room.