Any revenue bonds issued by the board under this subchapter may be refunded, and in that case all pertinent and appropriate provisions of this subchapter are applicable to the refunding bonds. In refunding any of the bonds the board may, in the same authorizing proceedings, refund bonds issued under this subchapter and may combine all the refunding bonds with any other additional new bonds to be issued under this subchapter into one or more issues or series of bonds, and may provide for the subsequent issuance of additional parity bonds, or subordinate lien bonds, under terms and conditions set forth in the authorizing proceedings.