Cal. Rev. & Tax. Code § 24351
Where, under regulations prescribed by the Franchise Tax Board, the taxpayer and the Franchise Tax Board have, after the date of enactment of this section, entered into an agreement in writing specifically dealing with the useful life and rate of depreciation of any property, the rate so agreed upon shall be binding on both the taxpayer and the Franchise Tax Board in the absence of facts or circumstances not taken into consideration in the adoption of such agreement. The responsibility of establishing the existence of such facts and circumstances shall rest with the party initiating the modification. Any change in the agreed rate and useful life specified in the agreement shall not be effective for taxable years before the taxable year in which notice in writing by certified mail or registered mail is served by the party to the agreement initiating such change.
Ca. Rev. and Tax. Code § 24351