Originally Posted by Happy

Did this countless time - the key is at check in, inform the FD that there is a reservation the following night, booked under different account, and asked the FD to assign same room so no need to move. Some hotels would not even need you to do the physical check out / check in again. But if you want to make sure each account gets its night / stay count, esp for elite status / benefit, you want to do a "clean" process, but still no need to change room. FD just do the formality, reprogram your keys, that is all being needed.

Matter of fact, we almost always book individual nights even for multiple nights stay, all from same account - this preserves the flexibility when plan changed and we needed to shift dates / cancel a night at the front / in the middle / at the end, however the plan change required. Much much easier to handle than booking a multiple nights stay as single reservation. The only time we do that is for the 5th night free point booking as that is the only way to get the one free night (although it is no longer the 5th night, but the cheapest night during the whole 5 nights stay, just make sure no misunderstanding here.)