The governing board may amend a previously adopted resolution ordering the formation of a school facilities improvement district to change or add to the purposes for which the school facilities improvement district is formed and the projects to be financed and to increase or decrease the amount of bonds that may be issued for those purposes. Bonds may be issued only for the purposes stated in, and in an amount not exceeding the amount stated in, a proposition submitted to and approved by the voters of the school facilities improvement district.