I have "linked" successive reservations from two use years a number of times over the last fourteen years. I have never had to change rooms when that was done. In the earlier part of those fourteen years, they did require you to go to the front desk on the turnover day and check-in to the room again. I have not had to do that anytime during the last six years. What may still occur is that they close out the bill for the first use year reservation on the turnover date and start a new one under the other use year, but you need not do anything when that occurs. Each use year reservation is treated separately for reserving at 11 or 7 months out. Also, the restaurant reservation period (pre-pandemic 180 days, now just 60), began separately for each use year reservation. Likewise, fast-pass (pre-pandemic, there is none right now) reservations had separate 60-day out periods.
Also, be aware that if there is any possibility you may change one or both of the reservations, such as switching them to a different resort at 7-months out, you should avoid linking them until after the 7-month window passes, because once two reservations are linked, it is impossible to cancel or modify either of them online and you have to first contact MS to unlink the reservations.