For National Federation:

A player has been removed from the game in a regular legal substitution. Is he now a eligible courtesy runner for the pitcher/catcher or does he have to reenter in the same spot he was removed from?

Players who have participated in the game in any other capacity are ineligible to serve as courtesy runners.

Also a courtsey runner may not enter into the game in the same half inning that he has been a courtsey runner, unless a player is forced to leave the game (injury, ejection ect.) and no other subustitues are available.