The regulations, restrictions, and boundaries may, from time to time, be amended, supplemented, changed, modified, or repealed. Notwithstanding section 414.2, as a part of an ordinance changing land from one zoning district to another zoning district or an ordinance approving a site development plan, a council may impose conditions on a property owner which are in addition to existing regulations if the additional conditions have been agreed to in writing by the property owner before the public hearing required under this section or any adjournment of the hearing. The conditions must be reasonable and imposed to satisfy public needs which are directly caused by the requested change. In case, however, of a written protest against a change or repeal which is filed with the city clerk and signed by the owners of twenty percent or more of the area of the lots included in the proposed change or repeal, or by the owners of twenty percent or more of the property which is located within two hundred feet of the exterior boundaries of the property for which the change or repeal is proposed, the change or repeal shall not become effective except by the favorable vote of at least three-fourths of all the members of the council. The protest, if filed, must be filed before or at the public hearing. The provisions of section 414.4 relative to public hearings and official notice apply equally to all changes or amendments.