"The First Circuit in United States v. Hilario, 218 F.3d 19 (1st Cir. 2000), similarly recognized that “[s]hould the stand-in” for a principal officer “remain so long in office that he became indistinguishable from the latter, an argument could be made that his continued service required nomination by the President and confirmation by the Senate.” Id. at 29."
So that is why - in Baseball - the coach/manager needs to change the line up card when a player is "subbed" for and that person can not return later ... hhmm