Hi Suzy. Click here
for Royal Caribbean's Terms and Conditions for shore excursion bookings. I don't see a cancellation penalty mentioned in the language if you should rebook onboard prior to the general deadline established for the tour. I'll leave it to someone who has done this recently (or who has been onboard recently) to confirm.
As for the Mystery Dinner, the cancellation policy is located here
. If you cancel onboard (or within 10 days of sailing), the refund will be in the form of a shipboard credit. There's a penalty for cancelling within 24 hours notice.