When I turned down my seat at SUNY, I actually had a conversation about this with Dr. Johnston. He was disappointed that I was turning down my seat but he knew I was still unsure about my decision (I was giving up the acceptance because I didnt want to take up the seat from someone who really wanted to go there). He told me if I changed my mind about relinquishing my seat, I could call him back and then be placed on the wait-list. The school could not automatically reaccept me but the best they would be able to do was put me on the wait-list with the least priority (to be fair to everyone else). Im not sure if they do this in every case but you can always call the schools you are concerned about and ask.