Once they sign, they are locked in until released. That is why most coaches will be fired before the early signing period begins. If it seems more difficult for programs who change coaches like they are changing their socks, it is suppose to be. Hire the right guy, treat him right, and don't have years where recruiting suffers. Something to be said for stability, and it's a wonder any of us can still spell that word.
This has been happening in basketball for years. Players sign in the fall, and their coaches sometimes get fired or hired away to bigger jobs in the spring. The school then almost always allows the players to be released from their LOIs if they choose. Still a month until NSD. That's enough time if the players want to be released