I think I understand the logic behind your question, and the answer is that hotels do oversell so there is the possibility that if you were to cancel your cash room that it doesn't go back into the inventory right away (so you might not be the first to snatch it back) or perhaps ever. There's a decent chance you'll be ok, but it's certainly not 100%. This does beg the question, can you book 10 base rooms at cash rates and then cancel them all to increase your odds of a points booking? Perhaps, but then you are also getting into breaking the T&C and this type of move might draw some attention. So I dunno what to tell you other than, you'd be taking a risk any way you approach it.