Section 50. A stock company may amend and restate its articles of organization as provided in sections seventy, seventy-one and seventy-four of chapter one hundred and fifty-six B, subject to the provisions of sections forty-eight and seventy-one of this chapter. A stock company by a two thirds vote of all its stock entitled to vote, at a meeting duly called for the purpose, may authorize an amendment of its articles of organization to alter, add to or change, to the extent authorized by this chapter, the classes of insurance for transaction of which it is incorporated and to provide for the transaction of insurance on a participating plan.