The boundaries of any irrigation district now or hereafter organized under the provisions of this act may be changed in the manner herein prescribed; but such change of the boundaries of the district shall not impair or affect its organization, or its rights in or to property or any of its rights or privileges of whatsoever kind or nature, nor shall it affect, impair or discharge any contract, obligation, lien or charge, for, or upon which it was or might become liable or chargeable had such change of boundaries not been made; provided, that if the secretary of the interior shall give his assent to a change in boundaries in writing filed with the board of directors, any lands to the exclusion of which from the district assent shall thus be given, shall be discharged from any and all liens in favor of the United States under any contract which shall have been made with the United States and any bonds deposited with its agents.