Cal. Rev. & Tax. Code § 24633

If a taxpayer changes its annual accounting period, the new accounting period shall become the taxpayer’s taxable year only if the change is approved by the Franchise Tax Board. For purposes of this part, if a taxpayer to whom Section 24631(g) applies adopts an annual accounting period (as defined in Section 24631(c)) other than a calendar year, the taxpayer shall be treated as having changed its annual accounting period.