(a) 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 signed after default.

(b) 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 signed after default.

(c) 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 signed after default.