(a) Waiver of disposition notification. A debtor or secondary obligor may waive the right to notification of disposition of collateral under Section 9-611 only by an agreement to that effect entered into and authenticated after default.(b) Waiver of mandatory disposition. A debtor may waive the right to require disposition of collateral under Section 9-620 (e) only by an agreement to that effect entered into and authenticated after default.(c) Waiver of redemption right. Except in a consumer-goods transaction, a debtor or secondary obligor may waive the right to redeem collateral under Section 9-623 only by an agreement to that effect entered into and authenticated after default.