The inclusion of an organized district into a consolidated district shall not affect or impair any bonds or obligations of such included district and the holders of the bonds of any such included district shall be entitled to all remedies for the enforcement of the same as if such district had not been consolidated, and all obligations that shall have been incurred by any district prior to its being included in a consolidated district shall be a prior lien to any obligation that may be incurred against such land under such consolidated district: PROVIDED, HOWEVER, That the board of directors of the consolidated district may when authorized thereto, exchange any bonds of the consolidated district for the bonds of such included districts upon obtaining the consent of such bond holders. If any included district shall prior to the time of its inclusion into a consolidated district have entered into any contract with the United States pursuant to the provisions of this chapter, and the board of directors of such consolidated district propose to enter into a contract with the United States by the consolidated district, said board of directors, when authorized thereto, shall enter into such contract with the United States, and may in such event, with the consent of the United States, cancel any contract previously entered into between any included district and the United States.