Section 9--624. Waiver. (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.