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 a full value assessment in the
assessing unit 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.