Notwithstanding any provision of the general statutes or special act 01-1, no municipality or special taxing district that provides, as of July 11, 2007, a pension and retirement system for its officers and employees and their beneficiaries shall diminish or eliminate any right or benefit granted to any retiree under such retirement or pension system that was in effect on the date of such retiree’s retirement. The provisions of this section shall not be construed to prohibit a municipality or special taxing district from changing the administration of such retiree’s retirement benefits as long as the rights and benefits provided to such retiree after any change in the administration are at least equivalent to the rights and benefits provided prior to such change.