Any district which has an existing contract with the Secretary as of October 12, 1982, which does not enter into an amendment of such contract as specified in subsection (a) shall be subject to Federal reclamation law in effect immediately prior to October 12, 1982, as that law is amended or supplemented by sections 209 through 230 of this title [43 U.S.C. 390ii—390zz–1, 373a, 422e, 425b, 485h]. Within a district that does not enter into an amendment of its contract with the Secretary within four and one-half years of October 12, 1982, irrigation water may be delivered to lands leased in excess of a landholding of one hundred and sixty acres only if full cost, as defined in section 390bb(3)(A) of this title, is paid for such water as is assignable to those lands leased in excess of such landholding of one hundred and sixty acres: Provided, That the interest rate used in computing full cost under this subsection shall be the same as provided in section 390ee(a)(3) of this title.

In the absence of an amendment to a contract, as specified in subsection (a), a qualified recipient or limited recipient may elect to be subject to the provisions of this subchapter by executing an irrevocable election in a form approved by the Secretary to comply with this subchapter. The district shall thereupon deliver irrigation water to and collect from such recipient, for the credit of the United States, the additional charges required by this subchapter and assignable to the recipient making the election.

Amendments to contracts which are not required by the provisions of this subchapter shall not be made without the consent of the non-Federal party.