A mutual company, by endorsement or rider approved by the Commissioner and sent to the policyholder, may simultaneously with or at any time after the adoption of a plan of conversion amend any outstanding insurance policy for the purpose of extinguishing the right of the holder of any such policy to share in the surplus of the mutual company. However, this amendment shall be null and void if the plan of conversion is not submitted to the Commissioner or, if submitted, is disapproved by the Commissioner or, if approved by the Commissioner, is not approved by the eligible members on or before the first anniversary of its approval by the Commissioner.