To switch over from a righty to a lefty is fairly easy. The reason why I say it's easy is because your dominant eye is closer to the pitch and your reaction speed is increased. Now, granted there are people whos dominant eye is opposite their batting style. A righty could have a left eye be their dominant eye. You also have to be skilled enough to transition the mechanics needed to move to the other side of the ball. Also i'm not an expert on batting but that's my take on the situation.