Section 19J. At any time before the plan of reorganization becomes effective as provided in subsections (a) to (n), inclusive, of section 19K, the mutual insurer may, by vote of a three-fourths majority of the board of directors, withdraw or amend the plan of reorganization. Any such plan amendment shall require the written consent of the commissioner. For a plan amendment, all references in sections 19F to 19W, inclusive, to the plan of reorganization shall be deemed to refer to the plan as amended, but no amendment shall be deemed to change the adoption date of the plan of reorganization. No amendment may change the plan of reorganization in a manner that the commissioner determines is prejudicial to the policyholders of the reorganizing insurer, unless a further hearing is held on the plan as amended, if the amendment is made after the initial public hearing, or unless the plan as amended is submitted for reconsideration by the members, if the amendment is made after the plan has been approved by the members.