This is a really good question. I'll be interested to hear what people have experienced.
I just went and read the terms and conditions on my room only reservation and they couldn't have been more vague. Just if eligible to modify, you'll see the button.
I called today and was today I could still modify the day before arrival but I know that sometimes misinformation is given. I’m hoping someone has experience or a definitive answer.
Good question. I changed hotels 24 hours prior in March. They keep changing stuff. Today I was able to add a person and pay the extra adult fee for December. I always had to call to do that in the past.
I would look online to see if you can. If not call and ask. They usually will let you move dates.