Courtesy runners were allowed until 1950.

What I suggested again in a recent post has precedent.  Players should be allowed to re-enter the game.

Pitchers hitting is an oxymoron. Designated FIELDER is the answer, along with re-entry and roster of 30. Thursday, April 30, 2015

re-entry within the confines of the batting order
____________________________

http://www.baseball-reference.com/bullpen/Pinch_runner

Courtesy Runners

In the early days of baseball, when rosters were much more limited, there were courtesy runners in addition to pinch runners. A courtesy runner was put in when the normal runner was temporarily incapacitated by an injury. A courtesy runner had to be agreed by the opposite manager, and his presence in the game was not considered as an official substitution. He could therefore be used again once his running duty was completed, or could be a player already in the line-up, and the player for whom he ran would usually return to the game in the next half-inning. In contrast with pinch runners, courtesy runners tended to be slow base runners. The last courtesy runner in a Major League Game was used in 1949 (list of all courtesy runners from Retrosheet)
_________________________

http://retrosheet.org/courtesy.htm

Courtesy Runners

Until 1950, a courtesy runner was allowed for a player if that player had been injured and at the moment couldn't continue. The original player then stayed in the game defensively in the next inning, although sometimes the injured player did not return. If the replacement runner was already in the game, we still count this as a courtesy runner. Most often the courtesy runner was already in the lineup. We also have four examples of courtesy fielders listed here...

8/10/1952 (Cubs at Pirates, game 2) - (COURTESY FIELDER) In the top of the ninth of the second game of a twin bill, Pirates catcher Clyde McCullough was injured and could not continue. The Pirates two other catchers, Eddie Fitzgerald and Joe Garagiola, had already been used in the game as pinch hitters. With the approval of Cubs manager Phil Cavarretta, Fitzgerald was allowed to replace McCullough. The Cubs won the game 4-3. Under the playing rules in effect since the 1950 season, that was an illegal substitution that the umpires should not have allowed.
_________________________

http://www.baseball-reference.com/boxes/PIT/PIT195208102.shtml

Ed Fitz Gerald PH-C