Let’s say it’s in the late innings, and the manager wants to make a pitching change. So he announces that Joe Blow will be coming out of the bullpen in relief. The opposing manager doesn’t like the Joe Blow vs. his guy matchup, so he names Jack Schmoe as a pinch-hitter. The first manager doesn’t like THAT matchup, so he names Jeff Doe as his relief pitcher.
So in this case, Joe Blow was announced, but never touched the ball.
Does he get credited with an appearance?
What if this was Joe’s first time in the big leagues, and he never gets announced again, and gets sent back to the minors at the end of the season, and never gets called up again? Does he still get credited as appearing in a game in the Baseball Encyclopedia (or whatever it’s called)?
However, the relief pitcher can’t be replaced until he has completed the plate appearance of one batter, the inning ends due to a pickoff or caught stealing, or he is injured and can’t continue.
The manager can’t opt to replace his reliever just because he doesn’t like the current batter/pitcher matchup. The offensive team can substitute batters all they want (& those substitute batters who are themselves substituted for get credited with a game played.) Larry Yount is the only player in the encyclopedias who didn’t actually play in any games.
Also if the pitcher were announced into the game and the game was suspended at that time, the pitcher could be replaced without facing a batter when the game resumes. However, he could not re-enter.