Switch Hitter's Rights

[Pallando]

Another player told me this and I'd like to know if it's true:

A switch hitter is in the middle of an at-bat (first pitch already thrown) and the batter decides to change sides. So he walks across or in front of the plate and takes his stance in the opposite box. My teammate says he's out because he must walk BEHIND the umpire and notify him he is switching batting sides.

Is this in any part true? If so,
* Does the ump just call him out?
* Must he be tagged?
* Must the other team protest first?
* Any other details to be considered?

Thanks.