When is a sub the pitcher?

[john5396]

So I think the rule I'm asking about is not 3.1.1 but 3.1.2.

If a pitcher is replaced while his team is on defense, the pitcher shall (complete the current at bat, paraphrase from the complete rule, please forgive me)...

When is he "replaced".

If the coach has a conference mid inning, takes the ball from the pitcher and gives it to the shortstop, when does F6 become F1 in terms of 3.1.2. In my neck of the woods, when there is just a position swap, the coach will not make a report of this change to the umpire. If previous F6 takes the rubber and starts warming up, is he required to face a batter? Or as UMPJM points out, he isn't the pitcher till the ball is placed in play. Could the coach watch old F6 warm up, decide after 5 warmup pitches that he doesn't have the "stuff" today and then give the ball to F4?

Ween does F6 become the new F1, and under 3.1.2 he is required to face one batter? When the coach hands him the ball?, When he starts throwing warmup pitches? or when warmup is complete and the umpire puts the ball in play?

So, the core of my question is, under 3.1.2, when is a pitcher "replaced"? My OP had the additional detail that the potential new pitcher was a potential unreported sub, but since ball has not been put in play, it is nothing and the coach pulled him back off the field before the ball was made live or he was reported, so that was nothing.