You saw the official rules…..
What I have done is booked the first 3 nights using cash or points and upgraded to a suite using cert. Then 4th night using a cat 4 cert that is expiring soon on a separate booking knowing we may have to move room on day 4. I asked WoH to note my free night confirmation in the first booking so hotel can see the back to back stays. In 2 occasions that I can think of, hotel extended the curtesy and we didn’t have to change room. YMMV.