Casinos generally cannot change the rules in the middle of a blackjack game. The rules are established before the game starts and must remain consistent throughout. Any changes would typically apply to future sessions, not to ongoing hands. While casinos may correct dealer errors during a hand, rule changes would not be made mid-game as it could be seen as unfair to players. Temporary promotions or rule variations can exist, but they are usually announced ahead of time and apply to new games or hands, not those already in progress.