Depends if it's there's promotional OBC -those may go away if you reprice. You keep the on board booking OBC if you reprice.
Ask your TA if she offers group rates - those are refundable and could be lower than the regular price.
At the bottom of the main screen, there should be a link to browse other ships - you can set the app to any ship in the fleet for about 90 days before sailing.
Get to the pier after the rush (have lunch some place on land away from the port), typically after 1PM, and do the same on debarkation day (after 9AM). Skip the Key.
For MTD, you can usually book dining times as soon as they are available in the planner (many times 1+ year out). Or, you can go to the MDR host on boarding day and arrange something.