Sure can...Several years ago I had a mini suite on the Rhapsody and when checking in at dock was told I had an owner's suite. Fantastic cabin. Only problem is in retrieving your luggage which is at your original b ooked cabin. I didn't mind the sacrifice.
booked way in advance specific cabin number. 5 months before sailing, TA called, we had been upgraded.
I guess since it was so early, we did not have the problem with our luggage ending up at the upgraded cabin.
I just got upgraded because I called my TA after seeing that the cruise prices had gone down. She called me back after talking to Carnival and they upgraded us. When we booked we had a confirmed cabin number, so it is possible. We are hoping that since we don't have any cruise documents yet (Dec. 9 sailing) that the luggage tags are changed accordingly.
I like your story about getting upgraded at the port, I sure hope that will happen to us. A girl can wish.