Sec. 8.4. Except as provided by an enactment of the general assembly, an election by an employer under:
(1) section 8(f) of this chapter concerning the payment of a retired employee's premium; or
(2) section 8(j) of this chapter concerning Medicare coverage and program eligibility;
may not be revoked or altered at any time by the employer or a subsequent employer to the detriment of a person entitled to benefits under section 8.2 of this chapter.