Changing a double to twin after booking
 

Hi all,
I am not very familiar with Marriott, being more of a Hilton/IHG person. I am trying to book 3 rooms at a hotel - two doubles and one twin. It appears this can't be done at the hotel I'm interested in (Sheraton Pretoria), and I have to choose one room type for all rooms. Normally, I'd just make two bookings, but in this particular instance I'm trying to make use of an Amex offer which requires certain spend in a single transaction.
Are there generally any issues with changing a room type after booking? Both rooms are the same price.
Thanks.

This should be a non-issue. You just need to contact the hotel, not Marriott, directly.

If OP doesn't have any status with Bonvoy, I don't think bedding type is guaranteed. OP should try to get a written confirmation from the hotel that OP's party will get two doubles and one twin (which I assume means a room with two twin beds).

I'd assume bedding is not guaranteed in hotels where you book a room and choose a preference for king/queen/two beds. In this particular hotel, they're both listed as separate types of rooms.