Hello Colleen, thanks so much for your question. Although I have not experienced the Disney Cruise Line yet, I have seen many pictures that my Moms Panel friend and DCL specialist Tracy has taken. She is definitely one that goes all out and decorates her door and walls on the ship.
In my experience, I have not seen people decorate doors at Walt Disney World Resorts as much as I have seen them decorate windows. There have been many times that I have been on a walk to my room and have seen some really creative and festive window displays. I thought that they were so neat that I decided to decorate our window last year to celebrate my son's 5th birthday. He woke up to see the window full of colorful decorations and he loved it. Mousekeeping also got into the fun and added towel animals to the window and arranged his Disney character toys each day.
I just recently answered a question about Walt Disney World Resort Hotel
window decorating so if you want you can go and check that out.
I think that decorating your Resort Hotel window would be a really fun way to show your creativity and also spread some magic to other guests. I'm sure you can also decorate your door as long as you are careful not to cause any damage to the property or chip any paint.
Have so much fun decorating, and if you need anything else, please let us know. Have a magical Walt Disney World vacation!