pinniped

I think the OP is saying he has the points right now for a Cat 5, but might later actually want to stay at a Cat 6 or 7. Could he then just pony up the extra 30k or whatever and book the Cat 6 hotel? The 120k US would have been converted long in the past (e.g., now) and the Cat 5 e-cert would be sitting in his account.

I honestly don't know. I've redeemed Cat 6 Travel Packages without a clue what hotel I was going to visit. In the end, I actually picked a Cat 6. This was when 7 was the top, and I knew we weren't going to NYC or London, so I figured 6 was safe. I think if I booked a TP blind now, I'd book 7 if I had the points.

I'm pretty sure you don't get a refund if you book a category down, but I don't know if Marriott makes it easy for you to add a few points and book a category up.