Let us know if it works out. Generally there ARE penalties unless the cruise is more than three to five months out, even if you are not in Early Savers.
They have Early Savers for a reason - so people have a chance to get lower fares. If it was as easy as you describe (just cancelling and rebooking) then they wouldn't need the price guarantee.
I am the editor, but I also speculate, ask questions and play devil's advocate. I reserve the right to change my mind.