Participation in the program by an irrigation district is voluntary and no irrigation district may be required to sell its municipal security issues to the program. Notwithstanding any other law, an irrigation district that wishes to participate in the program may enter into an agreement with the program for the purchase by the program of a municipal security issue of the irrigation district, including the purchase by the program of an issue of refunding municipal securities, which may be required by agreement with the program to be issued at a rate of interest higher or lower than that of the municipal security issue to be refunded.