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.