(a)   All existing annual pension acts are hereby repealed except that such acts shall continue in force with respect to persons already receiving annual pensions and with respect to present employees not disqualified by law or by ordinance from receiving annual pensions under such acts.
   (b)   The retirement system may be amended by the Trustees of the City Retire-ment System to meet the requirements of a qualified trust within the meaning of section 401(a), and to qualify as a governmental plan within the meaning of section 414(d) of the United States Internal Revenue Code of 1968, as amended, or replaced and with the laws of the state of New Hampshire.