§ 33. Election of certain optional retirement benefits by participating employers. By the adoption, filing and approval, where required,of a resolution in the manner provided by section thirty, section thirty-one or section thirty-two of this article, a participating employer may elect to provide for its own employees the benefit provided for persons in the employ of the state listed in subdivision j of section forty-one and may elect to provide the benefits provided for employees of participating employers in section sixty-b and section seventy-five-i of this article. Such election may be for a limited period if such limitation is included in the resolution, upon the expiration of which such election will be deemed revoked.