Every domestic mutual insurer shall promptly file with the Commissioner a copy, certified by the insurer's secretary, of its bylaws and of every modification thereof or addition thereto. The bylaws and modifications thereof shall be subject to the Commissioner's approval. The Commissioner shall not disapprove any such bylaw or modification unless found by the Commissioner, after a hearing held thereon, to be unlawful, unreasonable, inadequate, unfair or injurious to the proper interests or protection of the insurer's members or any class thereof. The insurer shall not, after receiving written notice of such disapproval and during the existence thereof, effectuate any bylaw provision so disapproved.