In any modification or refinancing of a debt secured by a mortgage or deed of trust on real property subject to Sections 89-1-301 through 89-1-329, the borrower and lender may contract and agree that all or any part of the accrued interest or interest to accrue or earned finance charge which has not been paid on the existing debt may be added to the unpaid principal balance thereof, and the borrower may contract for and agree to pay interest on the principal balance as modified as otherwise provided by law; provided, any such borrower shall have the right to prepay the original balance or the modified balance of the debt without penalty.