We just did this on the Dream last week and LOVED it!
We had the same stateroom so as a previous poster said, we didn't have to pack and were off and on the ship in a flash on turnover day. We did understand that this process is slightly different sometimes, but you will get a letter in your stateroom the last night telling you want to do.
We did request our serving team for the 2nd part of the B2B, and of course our stateroom host knew we were staying, but I was absolutely floored by the number of castmembers that recognized that we were "still here" on the 2nd leg! How do they do that??!!
A B2B 7 day sounds like a completely amazing thing and you now are my hero!
On our B2B it was the first time I sought out the laundry rooms on the ship. I thought this was a great way to fight my overpacking tenancies...so that would be a suggestion I would have for you to refresh your wardrobe during your trip.
Have a great time!