Bonds or notes issued for refunding purposes shall be authorized, issued, sold, approved and settled and refunding of lease rental debt shall be authorized and approved in the manner provided in this subpart for the authorization, issue, sale and approval of the original debt, subject to any additional limitations provided in this subchapter. No refunding bonds or notes shall be delivered to the purchasers thereof unless, simultaneously therewith, the notes or bonds being refunded become no longer outstanding in accordance with section 8250 (relating to use of proceeds of refunding bonds and when refunded bonds are no longer deemed outstanding). No adjustment in lease rentals shall be made unless appropriate provision for the retirement of the outstanding lease rental debt has been made.