The rules state that a player is eligible to be on the playoff roster if he is on the 25 man roster as of 8/31 at midnight. However, clubs can add a player to the playoff roster if another player is on the DL* provided that the added player is in the organization by 8/31. The restriction is that the player added must be a pitcher if the DL player is a pitcher, or a position player for position player. Within those restrictions, the ability to add players is pretty loose.

When (not if) the Tigers get to the playoffs, they will surely be moving one starting pitcher out of the rotation. They can either just add him to the bullpen and have eight relief pitchers, or they could add a position player and have an extra guy on the bench, whether that’s a catcher, an outfielder, pinch runner, or whatever. But they’d have to get the right roster balance by 8/31 in order to be able to add a position player later on.