If I sign a reaffirmation agreement, can it be different terms than the original contract?

The simple answer is yes – if you can get the lender/creditor to agree. A reaffirmation agreement is a new contract between you and the lender/creditor. If you must sign a reaffirmation agreement, I would encourage you to negotiate the interest rate, the balance owed, and/or the length of time to pay out the debt.