Cal. Gov. Code § 26332
An indenture may include a clause prescribing a procedure by which the terms and conditions of the indenture may be subsequently amended or modified with the consent of the board and the vote or written assent of the holders of a specified principal amount of the bonds issued and outstanding. Such clause may provide for meetings of bondholders and for the manner in which the consent of the bondholders may be given. The clause shall specifically state the effect of such amendment or modification upon the rights of the holders of all of the bonds and interest coupons appertaining thereto, whether attached thereto or detached therefrom.
With respect to any clause providing for the modification or amendment of an indenture, the board may agree that bonds held by the board, by any department, political subdivision or agency of the State of California, or by any public corporation, municipality, district or political subdivision shall not be counted as outstanding bonds, or be entitled to vote or assent but shall nevertheless, be subject to any such modification or amendment.
Pursuant to such a clause any amendment or modification may be made which is valid under the provisions of Section 26362 as it exists at the time such amendment or modification is made even though it might not have been valid under the provisions of that section as it existed at the time the bonds were issued.
Ca. Gov. Code § 26332