If a person has a green card gets divorced and it's conditional, can they remarry before the interview and get it instated with new spouse?

No. A green card is conditional on being married to the SAME person for the 3 years.

no ..... you start all over again ...

Trying to play the system is what that is called......... it is 'conditional' ONLY on remaining married to the person who sponsored the green card in the first place.......... so no, pack up and book a ticket home as if you have not remained married for 3yrs then you breach the 'conditions'

Consult an immigration lawyer to be sure.

It takes time for a divorce to finalize, but a conditional green card becomes invalid as soon as you split up/separate. Go home.