Desgnated Hitter is used for the Shortstop
DH will be called "Abel" and SS will be called "Baker"

MOVE #1
In the 3rd inning, DH Abel reaches base and the team terminates the DH role- Baker runs for Abel, remains in the game at SS and will bat when his turn comes up.

MOVE #2
In the 6th inning, Baker's spot is up, and the team RE-ENTERS Abel, claiming he is a starter re-entering. Please note he is entering not as the DH, but re-entering like any starter. Legal? If not, please point me to the rule that would regulate.

MOVE #3
Abel reaches base again, and the team RE-ENTERS Baker, claiming he was a starter who is entitled to re-enter one time. He started the game as the SS-designee, moved to SS when the team terminated the DH role, was removed for Abel, and now is re-entering. Legal? If not, please point me to the rule that would regulate.

Thank you.

Legal on all counts. As long as the batting order is not affected both players have re-entry rights.

Legal.