We have a custom filter block used in a custom EntryPromotion.  In the filter block we have 2 string fields where we can define skus included on this promo and brands included on this promo.  Our custom processors handle whether the promo will get fulfilled or not.  Is there a way to hook into the promo save event in the Commerce backend to change the sku values based on the entered brands?  For example, I'm removing BrandX.  OnSave, find all Skus that belong to BrandX and remove them from the Skus field and save.  thanks