We differ, but at least you're consistent.

Dash is right, Ozzy is right, and T is definitely right. You cannot tell the umpire that you are substituting for an offensive player who is 3 places down the order. He cannot be substituted for until it is his turn in the batting order. Here is how you correct the mistake: #20 batted for the player who was due up, and is now considered a legal substitution. That is who the coach meant that # 20 was batting for, not the guy down the line. The umpire should have spotted the coach's error and corrected it before the at bat. But since he didn't, he should correct it following the at bat, and just treat it like an unannounced sub.

Absolutely Dash is correct. And I for one WILL know were I am in the order when making an offensive change. The biggest reason is because we are not allowed to accept projected substitutions.

Maybe this will help explain why:
Say the coach says between innings, A will bat 4th this inning for D (D has no reentry left). 3 up three down inning follows so A doesnt bat. D goes back out to play defense. You will have a very hard time trying to explain why you wont let him stay in the game.

Yep, I agree with others on here. This simply becomes an unannounced, legal sub.

Play on, game over, whatever the PH did in his AB. The projected sub rule seems to protect the umpires in this sitch. Easy to solve...because for the most part, there's nothing to solve.