If any change or alteration of a contract governed by the provisions of this article is ordered by the governing board of the community college district, such change or alteration shall be specified in writing and the cost agreed upon between the governing board and the contractor. The board may authorize the contractor to proceed with performance of the change or alteration without the formality of securing bids, if the cost so agreed upon does not exceed the greater of:
(a) The amount specified in Section 20651 or 20655, whichever is applicable to the original contract; or
(b) Ten percent of the original contract price.