I would first checkout what the status of the new cabin is before put anything in the safe. Remember, once the B2B's clears Passport control and is free to go about your business it will be quite early, probably 1 hour before the new cruise embarkation. You won't know how far along the cabin attendant has made on the new cabin. If you go and checkout your new cabin and see all the drawers still open, closets open, bed unmade, I wouldn't put anything in the safe or in the closets.
That's why it wonderful when you can have the same cabin on a B2B.