Tex. Gov't Code § 855.607

It is intended that the provisions of this subtitle be construed and administered in a manner that the retirement system's benefit plan will be considered a qualified plan under Section 401(a) of the Internal Revenue Code of 1986 (26 U.S.C. Section 401). The board of trustees may adopt rules that modify the plan to the extent the board considers necessary for the retirement system to be considered a qualified plan. Rules adopted by the board of trustees relating to plan qualification issues are considered a part of the plan.