Any agreement reached between the board and the city or county, or city and county acting jointly, or authorized port or harbor agency shall be reduced to writing and set out the terms and conditions under which such planned development shall be completed, and shall specifically set out the maximum amount of bonds, if any, to be issued by the state for the completion of such planned development. No such agreement shall become effective until approved by a majority of the qualified electors of the city or county having jurisdiction of such port or harbor voting in an election called for that purpose in the same manner as in other city or county special elections. Any plan, agreement and contract which has been approved by the qualified electors of a county or municipality as herein provided, may be amended or supplemented to add additional projects thereto in the same manner as provided herein for the submission, modification and approval of the original plan, agreement and contract, save that instead of submitting such supplemental contract to the qualified electors of the county having jurisdiction of such port or harbor for approval, the governing body of the county or municipality shall, by the affirmative vote of two thirds (⅔) of all members of such governing body, adopt a resolution reciting the substantial terms of such supplemental contract and giving notice that such contract shall become effective on the date specified therein which shall be not less than twenty-five days from the date of the first publication of such resolution. Such resolution shall be published once a week for at least three successive weeks in the newspapers published and of general circulation within such county or municipality. The first of such publications shall be made at least twenty-one days prior to the date set forth in said resolution as the date upon which the supplemental contract shall become effective and the last of such publications shall be made not more than seven days prior to such date. If prior to the date set forth as aforesaid there shall be filed with the clerk of the governing body of the county or municipality a petition in writing signed by twenty per cent (20%) of the qualified electors of such county or municipality requesting an election on the question of whether or not such contract shall be effective, then such contract shall not become effective unless approved by a majority of the qualified electors of the county or municipality who vote therein at an election to be ordered by the appropriate governing body for that purpose. Notice of such election shall be given and such election shall be held and conducted in like manner as approved by law with respect to the submission of bond issues in the county or municipality. If the proposition so submitted shall fail to receive approval at such election, then such contract shall not become effective. If, however, no such petition shall be so filed, or if at such election, or subsequent election, such proposition be assented to by the majority of qualified electors voting therein then such contract shall become effective on the dates set forth in the resolution. Any such contract or supplemental contract shall require that any such city, county, or city and county acting jointly, or authorized port or harbor agency shall pledge all net revenues to be derived from the planned development to the payment of principal and interest on the bonds issued for such planned development, and shall further require such agency to pay the principal and interest on such bonds, and all premiums, fees, or other charges in connection therewith as the same shall mature or become due. The proceeds of any bonds issued for such planned development shall be expended only for the purposes set out in such approved contract. To meet the obligations imposed by this section, any such city, county, or city and county acting jointly, or authorized port or harbor agency is hereby authorized to appropriate therefor any surplus funds from any source available to said city or county, or both acting jointly, or to levy a tax therefor not to exceed five mills on all taxable property in said county or city, or both. The levies made under this provision shall not be reimbursed under the Homestead Exemption Law of 1946, being Sections 27-33-1 through 27-33-65, Mississippi Code of 1972. The ownership, operation and control of such planned development shall remain vested in the city, county, or other authorized port or harbor agency in such manner as is now or may hereafter be authorized by law.