(a) A county, school district, improvement district, or municipality may refund bonds issued under statutory or constitutional authority at any time outstanding by the issuance of bonds bearing a rate or rates of interest that the issuer deems to be just and fair, whether or not greater than the rate or rates of interest borne by the bonds being refunded.
(b) Bonds shall not be refunded at a rate of interest greater than the maximum rate set by the statutes or constitutional provision under which the bonds were originally authorized.