If you need to move a reservation, you should always try to keep OTA bookings in rooms of the same type as they were booked in. Here's why.
Let's take a fictional 2 bedroom hotel, with a single and double room.
We get an OTA booking for a single room. It is imported correctly into Room 1.
We give the guest a free upgrade to a double room, and move them into Room 2. In the next few days, someone books our single room and so the property is full on those dates.
The guest makes a minor change to their OTA reservation - it might be simply to request an early or late checkin or update their card details. The OTA forwards the modification, and in the booking details sent to the channel manager specify that "THIS BOOKING IS FOR A SINGLE ROOM".
We are required to try and drop that booking into a single room. But our only single room is now occupied by a different guest. So now, the booking is parked on the shuffle row.
If you aren't quick and drop that back into Room 2, you have the potential for Room 2 to be now open and available across your frontdesk, web and OTA's, and if it were to be booked, our first guest would be without a room.
Why can't we ignore the Room type and leave the booking for the Single Room left in the Double room?
Because if we extend this principle to a larger property with Room 3 as a twin, how would we know when the guest had added a second person to the booking at the OTA, and agreed to pay £20 more for a twin room? The modification tells us "THIS BOOKING IS FOR A TWIN ROOM". But if we ignored that, then two work colleagues arrive to be shown to their double room...
Channel managers are required as part of their certification process to modify existing bookings from OTA's as per the details in the modification.
If your guest wants to change room type, then you should advise them to do so directly at the OTA, and Caterbook would handle the change message sent by the OTA.
If you want to change room types for reasons of increasing your occupancy then you have to understand the possible implications and watch out for any additional changes being made at the OTA.