With the new guy on the block, Pat Venditte I went to look for a definite rule and believe me there are many rules but nothing that was definite via the web that is.

I was surprised in what I found in that the pitcher and batter are allowed to change their preferences once during there "at bat/at pitch:

Legal rule as below:

The new rules regarding ambidextrous pitchers are as follows:
• The pitcher must visually indicate to the umpire, batter and

runner(s) which way he will begin pitching to the batter. Engaging

the rubber with the glove on a particular hand is considered a

definitive commitment to which arm he will throw with. The batter

will then choose which side of the plate he will bat from.
• The pitcher must throw one pitch to the batter before any "switch"

by either player is allowed.
• After one pitch is thrown, the pitcher and batter may each change

positions one time per at-bat. For example, if the pitcher changes

from right-handed to left-handed and the batter then changes batter's

boxes, each player must remain that way for the duration of that at-

bat (unless the offensive team substitutes a pinch hitter, and then

each player may again "switch" one time).
• Any switch (by either the pitcher or the batter) must be clearly

indicated to the umpire.
• There will be no warm-up pitches during the change of arms.
• If an injury occurs the pitcher may change arms but not use that

arm again during the remainder of the game.