Such regulations, restrictions and boundaries may from time to time be amended, supplemented, changed, modified or repealed. In case, however, of a protest against such change signed by the owners of thirty-three and one-third per cent or more, either of the area of the lots included in such proposed change or of those immediately adjacent to the rear thereof extending one hundred feet therefrom, or of those directly opposite thereto, extending one hundred feet from the street frontage of such opposite lots, such amendment shall not become effective except by the favorable vote of two-thirds of all the members of council.