Switching staterooms, I would give the stateroom attendant a heads up on the first leg when you first meet him/her. The stateroom attendant will remove all your clothes hanging in the closet. Your responsibility is to pack every thing else up and have it all ready for the losing or gaining stateroom attendant to move it to your new Stateroom. We always have the same stateroom for both legs and the stateroom attendants always knows we are consecutive cruisers.
Cruise lines don't sell B2B cruises. You purchase two different cruises. Not a biggie filling out the pre-boarding info, again. Select any time for check in as it's not required for the second leg. I always print the Express pass for each leg. I've never needed the second one. You or the Celerity agent or your TA can't link them as far as the Express passes. I wish it was set up that way. You are consider consecutive cruisers and our experiences is the ships staff knows that by your reservation numbers. We have never gone to GS while on the ship and pointed that out to them that we are B2B'ers. We've never been kicked off the ship at the end of the first leg.
If you have any NRD OBC spend it or you will lose it. Refundable OBC doesn't carry over either. It will be credited back yo your credit card on file. Nothing carries over from the first leg to the second leg. Your onboard account account will be closed at the end of the first leg.
Bottom line is you will receive a detailed letter in your stateroom a day or two prior to TAD on the entire TAD process. All of our B2B cruise have gone seamlessly. Enjoy. 🍻