Public Contract Code § 20136

Whenever the board enters into a contract for the erection, construction, alteration, or repair of any public building or other structure, the contract shall not be altered or changed in any manner, except:

(a) As provided in Section 20142.

(b) As provided for in the contract itself, or specifications.

(c) By order adopted by a vote of two-thirds of the board, and the consent of the contractor.