Sec. 3A. CERTAIN ALTERATIONS BY LOCAL AGREEMENT. (a) Except as provided by Subsection (b) of this section, the board is authorized, on behalf of the members or beneficiaries of the fund, to alter benefit types or amounts, the means of determining contribution rates, or the contribution rates provided under this article if the alteration is included in a written agreement between the board and the municipality. An agreement entered into under this section:

(1) must:

(A) if the agreement concerns benefit increases, other than benefit increases that are the result of Section 13E of this article, adhere to the processes and standards set forth in Section 10 of this article; and

(B) operate prospectively only; and

(2) may not, except as provided by Sections 13A through 13F of this article, have the effect or result of increasing the unfunded liability of the fund.

(b) In a written agreement entered into between the municipality and the board under this section, the parties may not:

(1) alter Sections 13A through 13F of this article, except and only to the extent necessary to comply with federal law;

(2) increase the assumed rate of return to more than seven percent per year;

(3) extend the amortization period of a liability layer to more than 30 years from the first day of the fiscal year beginning 12 months after the date of the risk sharing valuation study in which the liability layer is first recognized; or

(4) allow a municipal contribution rate in any year that is less than or greater than the municipal contribution rate required under Section 13E or 13F of this article, as applicable.

(c) If the board is directed or authorized in Sections 13A through 13F of this article to effect an increase or decrease to benefits or contributions, this article delegates the authority to alter provisions concerning benefits and contributions otherwise stated in this article in accordance with the direction or authorization only to the extent the alteration is set forth in an order or other written instrument and is consistent with this section, the code, and other applicable federal law and regulations. The order or other written instrument must be included in each applicable risk sharing valuation study under Section 13B or 13C of this article, as applicable, adopted by the board, and published in a manner that makes the order or other written instrument accessible to the members.