[pob14]

Originally Posted by jicecone

The substitute officially becomes the new pitcher after he has thrown a pitch. Not necessarily when he takes his place at the mound.

Seems clear to me:

Originally Posted by Da Roolz

3.08
(a) If no announcement of a substitution is made, the substitute shall be considered as having entered the game when—

(1) If a pitcher, he takes his place on the pitcher’s plate;

I don't see any ejection authorized either; looks like it's a "fix it":

c) If an improper substitution is made for the pitcher, the umpire shall direct the proper pitcher to return to the game until the provisions of this rule are fulfilled. If the improper pitcher is permitted to pitch, any play that results is legal. The improper pitcher becomes the proper pitcher as soon as he makes his first pitch to the batter, or as soon as any runner is put out.

Rule 3.05(c) Comment: If a manager attempts to remove a pitcher in violation of Rule 3.05 (c) the umpire shall notify the manager of the offending club that it cannot be done. If, by chance, the umpire-in-chief has, through oversight, announced the incoming improper pitcher, he should still correct the situation before the improper pitcher pitches. Once the improper pitcher delivers a pitch he becomes the proper pitcher.