Notwithstanding any other provision of law, within the Rainbow Municipal Water District, if bonds have been authorized or issued pursuant to

Chapter 4 (commencing with

Section 71920) of this part, and thereafter, due to a change in conditions or circumstances, the board determines that the improvement, generally described in the resolution of intention No. 438, adopted October 27, 1969, pursuant to

Section 71924, should be significantly modified, the board by resolution may so modify such improvement and may issue authorized but unissued bonds or, to the extent the rights of bondholders are not impaired, expend the proceeds of bonds issued for the purpose of paying the cost of the improvement as modified, without any further election or without taking proceedings pursuant to

Chapter 4 (commencing with

Section 71920) of this part, provided that such modification shall not change the purpose for which the sale of bonds was originally authorized, and only after notice and hearing in the same manner as provided in

Article 2 (commencing with

Section 71880) of

Chapter of this part and

Article 6 (commencing with

Section 53520) of

Chapter 3,

Part 1, Division 2, Title of the Government Code, and provided that at the conclusion of the hearing the board, four-fifths of the members concurring, shall by resolution determine that the territory within the improvement district will be benefited by the improvement as modified. Notwithstanding the foregoing, the board, by resolution, may make minor modifications in the plans for the acquisition and construction of improvements and the determination made in such resolution shall be final and conclusive.