A. A debtor or secondary obligor may waive the right to notification of disposition of collateral under section 47-9611 only by an agreement to that effect entered into and authenticated after default.B. A debtor may waive the right to require disposition of collateral under section 47-9620, subsection E only by an agreement to that effect entered into and authenticated after default.C. Except in a consumer goods transaction, a debtor or secondary obligor may waive the right to redeem collateral under section 47-9623 only by an agreement to that effect entered into and authenticated after default.