If I understood correctly, some have reported only having to pay port fees and taxes when their guarantee category cabin sells out. Not the OP but others.
Ask an officer in the Windjammer for what you are looking for. Ham and cheese between 2 slices of bread. Add tomatoes and condiments off the bar. I have found them very accomodating.
Sort of happened to me once. We were called to Guest Services day 1. They said I was in a cabin with the wrong person of my wife's name. The other person assigned to our cabin had same exact name but different ca #. When they realized their mistake they said they could get it get it all straightened out in the back. I said, why not bring the other gal down and let me pick. (My wife of 50+ years gets my off beat humor and was not offended. )
I doubt it. If so they might as well just charge everyone the discounted rate and save all the time/trouble refunding every booked cruise that is less on black friday.