A contract is a legally binding document between you and the Seller. All of the terms have been agreed upon including the deposit, down payment, and financing terms. If there is a change to any of the terms, both parties must be notified and they must agree (addendum to contract). If a term changes and both parties are not notified and agreed, you could technically be in breech of contract. If you do complete the sale and close, probably nothing would happen. If however, you are unable to get financing, you have changed the financing terms and could be in jeopardy of losing your deposit. The best bet is to create an addendum with the new terms and both you and the Seller should sign.