I am assuming that the REPEAL LAW card only affects existing laws that are already in play, But can the card be used to stop an Agenda before it becomes law. I am thinking NO, but there was some dispute over the use of the card.

Agenda's don't become law's until they are passed.

Repeal is to Laws what Veto is to Agendas.

tricky question
There is a law which adds extra obj to public pool.
Lets say 2 of 6 players scored it.

Then repeal the law is played. DO these players loose VP from that extra obj?

We played it the way that noeone else can score it but VPs are staying.