As long as you're still within the option period you can re-negotiate with the confidence of knowing that you can still walk-away from the contract if you cannot come to an agreement with the Seller. If you're no longer in the option period, you can still negotiate, but the Seller doesn't have to agree to any changes to the contract.
Typically, the things you might be re-negotiating include: changing the closing date, adding/removing items from the repair list, and negotiating what items will stay with the home.
As you're Realtor, I'll be tracking all the key dates to make sure that you have the strongest negotiating position possible and that both sides are meeting all the key contractual dates. I'll also craft the documents to ensure you get all the items you are entitled to.