Any other provision of this chapter to the contrary notwithstanding, to the extent that the Board of Trustees of the Georgia Municipal Employees Benefit System created by Chapter 5 of this title has adopted a plan document or rules and regulations that are in compliance with Sections 401(a) and 414(d) and other applicable sections of the federal Internal Revenue Code, such plan document or rules and regulations shall govern such system notwithstanding any conflicting provision in this chapter; provided, however, that the provisions of Code Section 47-1-13 shall in any event apply to said system.