Section 4. All corporations existing on October first, nineteen hundred and sixty-five and their directors, officers and stockholders shall be entitled to all the rights, privileges and immunities and be subject to all the liabilities set forth in this chapter to the same extent as corporations formed under this chapter and their directors, officers and stockholders; provided that this chapter shall not take away or impair any remedy which may exist by law against a corporation existing on said date, its directors, officers or stockholders, for a liability incurred prior thereto.