The board, without further authorization from the legislature, may provide for the issuance of revenue bonds (herein referred to as refunding bonds) for the purpose of refunding, redeeming, or retiring at or at any time before maturity or at any time before the first date upon which the outstanding bonds to be refunded may be called for redemption, any bonds issued under this part, including any bonds which the holders may consent to be paid or refunded even though the bonds are not matured or are not callable or redeemable, and for the purpose of funding indebtedness not evidenced by revenue bonds but which was incurred for purposes for which revenue bonds may be issued pursuant to this part. The rate or rates of interest borne by the refunding bonds shall not be affected or limited by the rate or rates of interest borne by the bonds to be refunded or the indebtedness to be funded. All provisions of this part applicable to the issuance of revenue bonds shall be complied with in the issuance of refunding bonds. Refunding bonds shall be sold as provided in § 10-25, or the board may, in its discretion, provide for the exchange of refunding bonds for a like principal amount of outstanding bonds for the refunding of which the issuance of such refunding bonds has been authorized, whether or not the interest rate on the refunding bonds is higher than the interest rate on the bonds refunded thereby.