Subject to such terms and conditions and to such rules and regulations as the retirement board may adopt, any contributor from time to time may:
1. Increase or decrease his or her rate of contribution to the annuity savings fund, but in no event shall the contribution of a present-teacher be less than the minimum contribution, nor shall the contribution of a new-entrant, other than a twenty-year pension plan contributor or an age-fifty-five-increased-benefits pension plan contributor, be at a rate less than the per cent rate provided for such new-entrant in section 13-521 (2) of this chapter, (relating to contributions of new entrants) nor, in the case of a twenty-year pension plan contributor, shall his or her effective contribution rate as a twenty-year pension plan contributor (as such rate is defined in subdivision forty-five of section 13-501 of this chapter) be less than that established for such contributor as provided in subdivision seven of such section 13-521, nor in the case of an age-fifty-five-increased-benefits pension plan contributor, shall his or her effective contribution rate as an age-fifty-five-increased-benefits pension plan contributor (as such rate is defined in subdivision forty-six of such section 13-501) be less than that established for such contributor as provided in subdivision seven of such section 13-521; provided that nothing contained in this subdivision shall deprive any contributor of a reduction in contributions to which such contributor may be entitled under the provisions of section 13-546 of this chapter;
2. If a present-teacher who is not a twenty-year pension plan contributor or an age-fifty-five-increased-benefits pension plan contributor, withdraw from his or her individual account in the annuity savings fund the amount in excess of his or her minimum accumulation;
3. If he or she is not a twenty-year pension plan contributor or an age-fifty-five-increased benefits pension plan contributor, withdraw, after having become eligible for service retirement, such part of his or her accumulated deductions as shall be in excess of the amount necessary to procure for him or her an annuity which, if added to his or her prospective pension and his or her pension-providing-for-increased-take-home-pay, if any, will yield a retirement allowance of fifty per cent of his or her average salary.
4. If he or she is a twenty-year pension plan contributor, withdraw, after becoming eligible for service retirement, such part of his or her accumulated deductions as shall be in excess of his or her minimum accumulation; provided, however, that any such contributor who makes an original or any subsequent withdrawal of any such excess or any part thereof shall not be entitled to make a further withdrawal of any such excess or part thereof during a period of one year after the last such withdrawal except that a contributor may make a withdrawal at the time of retirement regardless of any previous withdrawals.