Starting Pitcher Replaced Returns

[DG]

Situation. FED.

Starting F1 and F2 swap on 1st trip by HC in 2nd inning. After one batter they swap back on 2nd trip (neither one counted as conference since change made). Clearly a LH/RH situation going on here. After one batter they swap again on 3rd trip. I believe they can since a pitcher can return to pitch but only once in an inning. Now, is sub pitcher F1 treated the same and he can come back too? I see no distinction between starter and sub in 3-1-2, just says "A player." Can they do this again in a future inning? I know a pitcher, any pitcher, after removal after 3 trips can not return, but I can't find an interp to prevent defense from doing this in any inning as long as HC has trips left.