Idaho Code § 43-604
All or any part of such refunding bonds may be exchanged, dollar for dollar, for the bonds to be refunded, or they may be sold, at not less than their par value, as directed by the board of directors, and the proceeds thereof shall be applied only to the purposes for which said refunding bonds are issued. The authority vested in the board of directors by any election held pursuant to the provisions of this chapter shall be and remain effective until all of the bonded indebtedness so authorized to be refunded has been paid, redeemed or refunded. At the time of the issue, by exchange or sale, of refunding bonds authorized under the provisions of this chapter, each bond shall be registered by the treasurer of the district, in a book to be kept by him for such purpose, and interest thereon shall begin to run only from the date of such registration. Coupons evidencing unearned interest shall be detached and canceled. Each bond, so registered, shall bear thereon indorsed the treasurer's certificate of such registration, and only such bonds as shall bear such certificate shall be valid; but such certificate shall be conclusive evidence that the bond so certified has been duly issued in full conformity with the provisions of this chapter. All district bonds redeemed under the provisions of this chapter shall thereupon be canceled by the district treasurer, and a record of such cancellation made and preserved in the records of his office.
Idaho Code § 43-604