Mutual insurance companies, other than mutual life companies, may insert, in any form of policy prescribed by the law of this Commonwealth, any provisions or conditions required by its plan of insurance which are not inconsistent or in conflict with any law of this Commonwealth. Such policy, in lieu of conforming to the language and form prescribed by such law, may conform thereto in substance, if such policy includes a provision or endorsement reciting that the policy shall be construed as if in the language and form prescribed by such law; and a copy of such policy and endorsements, if any, shall have been first filed with, and shall not have been disapproved by, the Insurance Commissioner.