Looking for a Rule Reference

[Freddy]

NFHS Officials Manual:
"The warning signal does not affect substitutions on a player directed to leave the game, ie. disqualification, injury, blood. Substitutes may be granted until the player has been replaced and the ball is about to become alive."
(Though I don't know if this addresses the precise situation in question.)
(I'm waiting for someone to say, "Don't be a plumber", but I guess that retort only applies to questions I ask.)