No increase in the construction charges shall, after August 13, 1914, be made, after the same have been fixed by public notice, except by agreement between the Secretary of the Interior and a majority of the water-right applicants and entrymen to be affected by such increase, whereupon all water-right applicants and entrymen in the area proposed to be affected by the increased charge shall become subject thereto. Such increased charge shall be added to the construction charge and payment thereof distributed over the remaining unpaid installments of construction charges: Provided, That the Secretary of the Interior, in his discretion, may agree that such increased construction charge shall be paid in additional annual installments, each of which shall be at least equal to the amount of the largest installment as fixed for the project by the public notice theretofore issued. And such additional installments of the increased construction charge, as so agreed upon shall become due and payable on December 1 of each year subsequent to the year when the final installment of the construction charge under such public notice is due and payable: Provided further, That all such increased construction charges shall be subject to the same conditions, penalties, and suit or action as provided in sections 478, 480, and 481 of this title.