I'm not sure that the specific buildings are tied to check in dates.
When we checked in the woman at the desk asked if we were going to visit the parks. When we replied that no, we were just going to hang out at the pool she said she would "find us a room near the pool". And she did, perfect location! Seems she had some flexibility.
BTW, the reason we weren't going to Disney that week was because we had just spent 10 days at POR and we scheduled an additional week with our timeshare swap just to recover.