After taking advice from MRIs etc, I made a booking at West India Quay for December 2014 for 5 nights using points. I did not have enough points at the time (and won't for a few weeks), but as the hotel was going from 6 to 7, I made the reservation. Fortunately, I had the foresight to take a printout of the reservation which shows 120,000 points, which was made on 19th March. I agreed an upgrade price for the room, but this was on 24th March. I checked with Marriott at the time of booking about the points, saying
"I have made the above reservation, stating I will use Reward Points. I do not at present have quite enough points, but will have long before the arrival date.
The hotel is about to go from Cat 6 to 7, so I have booked at the old rate of 120,000 points for 5 nights before the cut off date of 7th April. Please confirm that my reservation will be honoured at 120,000 points once>I have sufficient points."
They replied in an email "Any reward redemptions booked before the category change will be honored at the category they were booked at."
I have made no amendments to the booking since. But today I was reviewing my upcoming bookings and it has been changed to category 7 and 140,000 points! So what happened to "we will honour all bookings etc"?
Also, I would suggest other MRIs check their advance points bookings as well.