Can an umpire change his decision?

Yes, an umpire can change their decision during a game if they believe they made an error or if new information comes to light, such as an appeal from players or assistance from other officials. However, such changes are typically rare and are subject to the rules of the specific sport being played. In some sports, like Baseball, umpires can consult with each other to clarify a call. Ultimately, the decision to change a call rests with the umpire's judgment and the established rules of the game.