Not sure exactly what you mean. EPs don't have to do anything to go in and out of any defensive position as long as both players maintain their position in the batting order, if they go in for the pitcher normal pitching substitution rules apply. You can substitute a player for the EP and then that player becomes the EP at that point it is just like any other sub they can only re-enter at that spot in the line-up as the EP again then you could re enter the sub again if you want.
Same basic re entry rule apply "any player may be withdrawn from the game and re entered once"
**This is PONY, but it sounds like they use the same rules**
If the EP stays in the batting order, they can sit on the bench or go in on defense at any position, and it does not count as a substitution.
If you replace your EP in the batting order with a substitute, the player who was your EP (and now a sub) has one re-entry, but they must replace the player who took their spot in the batting order.
From what I understand, you are allowed to have has many as 9 position players plus 2 EP's hit... Any more after that and they have to be listed as a sub... Its perfect if you only have 11 players, because then everyone can hit and you can swap the EP's with any of your positional players as much as you want... If you bat 9 then you must list them as sub's not EP's and then I believe they are "Married" to the player they sub with..