I have booked a 300k 7 night stay on points at Ritz Carlton Tenerife over New Year. I didn’t have the points when booking so made a reservation with the proviso of obtaining an e-certificate at a later date.
I am now thinking of going for a 7 night air hotel package instead. I should have enough points by late November. However by that time the bonus period for the 35% extra avios will be over.
What is the chance that I can book a 7 night hotel air package Marriott Cat 1-5 now then come November phone up Marriott and ask to upgrade that to a Tier 1-3 Rtiz Carlton air hotel package for my Tenerife stay thus at the same time applying the e-certificate to the 300k provisional points booking I currently hold.

Any advice is appreciated as I want to be certain before I do it as there is no longer any points availability for Tenerife!