[rcaverly]

NFHS 12-1-1

By state association adoption any, all, or any part of the suggested speed-up
rules may be used.

COURTESY RUNNERS
1. At any time, the team at bat may use courtesy runners for the pitcher and/or the catcher. In the event that the offensive team bats around, the pitcher and/or catcher who had a courtesy runner inserted on their behalf may bat in their normal position in the batting order.
2. The same individual runner may not be used for both positions (pitcher and catcher) during the game.
3. Neither the pitcher nor the catcher will be required to leave the game under such circumstances.
4. Players who have participated in the game in any other capacity are ineligible to serve as courtesy runners.
5. A player may not run as a courtesy runner for the pitcher or the catcher and then be used as a substitute for another player in that half inning. If an injury, illness or ejection occurs and no other runners are available, the courtesy runner may be used as a substitute.
6. The umpire-in-chief shall record courtesy runner participation and also announce it to the scorer.
7. A player who violates the courtesy-runner rule is considered to be an illegal substitute. [Again, my emphasis.]
a. Should an injury, illness or ejection occur to the courtesy runner, another courtesy runner for the pitcher or catcher may run.

This is hard to violate because the UIC won't permit the entry if the CR was previously used in the game for the other battery position and it was recorded on his (the official) line up card.

Again, all the angst during the game over the CR has likely mitigated the intent of the rule.