If the ratio between an exemption granted under § 458
of the Real Property Tax Law and the total assessed value of the real
property for which such exemption has been granted increases or decreases
due only to full value assessment in the Town of Sardinia in which
such real property is located, the amount of the exemption heretofore
or hereafter granted shall be increased or decreased in such subsequent
year in the same proportion as the total assessed value has been increased
or decreased.