Fed Substitution Rule

[sprivitor]

A few questions with Fed rule.

Starter S1 in game. Sub later enters game for S1. S1 on bench. Can S1 sub for another Starter?

Same question with Sub. When Sub comes out and S1 reenters game, can Sub later re-enter game for a different Starter?

Last Question: Sub1 enters game for S1. Sub later comes out of game. Can Sub2 enter game for Sub1?

Thanks in advance!