Cal. Pub. Util. Code § 25056

All persons receiving pension benefits from such acquired public utility and all persons entitled to pension benefits under any pension plan of such acquired public utility may become members or receive pensions under the retirement system established by the district as provided for in Chapter 5 (commencing with Section 25301) of this part, or participated in by the district as provided for in Section 25305 of this part, by mutual agreement of such persons and the district. Such agreement may provide for the waiver of all rights, privileges, benefits and status, with respect to the pension plan of such acquired public utility.