(2) The classifications and grades may, from time to time, be amended, added to, consolidated or abolished by the commission, but no person holding any position under any established classification or grade shall be affected by such change so as to deprive the person of any of the benefits attached to the classification or grade applicable to the position then held by the person. No person shall be promoted or advanced to a higher classification by such change without being eligible for appointment to such higher classification by reason of the position of the person on the promotion register. [1959 c.252 §26]