A few months back, I was one of the posters who received confirmation in writing that you can rewrite a contract as long as it hasn't closed yet. Back in June, my guide confirmed via email that you can rewrite to obtain better incentives up until it closes, so if you opt for the 90 day close, you have the full 90 days to do so. He also shared I could change resorts (at that time, I was debating Riv vs Poly).
Our 90 day close was a deposit, and then payments at 30/60/90 days, paying cash. The contract closed 90 days after we paid the deposit, which is also the day the final payment is taken. We agreed the specific 30/60/90 dates with my guide at time of finalizing the deal.
We actually did a contract rewrite approx. two weeks into the 90 days when a Disney Visa deal came out and I wanted the additional savings. No issues there. It didn't change the closing date, which was still 90 days from the original deposit date.
For anyone considering this, I would reconfirm with the guide that it is possible, and not bank on it either way. It isn't in the contract legal terminology, just via email from my guide. And policies can change.