I would like to add for
@daisyx3 :
In the past, I was told by someone from Carnival that if I kept all my guests "TBA" and have to cancel, I will only pay a 50$ fee --removed from the credit kept for 24 months-- when I do the change. I tested it and it worked. I've paid only 50$ fee instead of 50$ fee/pp (which used to be 100$/pp in my case).
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Also, when you book with Early Saver, you cannot "downgrade" your room category in order to save money. You can only upgrade.
That being said, if the price of the type of room you picked gets lower than it was when you originally booked, you can fill a price protection form and they will either upgrade your room or give you a refund in form of OBC. We got back 25$/pp on our last cruise thanks to that.