(9) Notwithstanding any other provision of law to the contrary, where a head of household holds a current, valid rent exemption order and, after the effective date of this paragraph, there is a permanent decrease in aggregate disposable income in an amount which exceeds twenty percent of such aggregate disposable income as represented in such head of the household's last approved application for a rent exemption order or for renewal thereof, such head of the household may apply for a redetermination of the amount set forth therein. Upon application, such amount shall be redetermined so as to reestablish the ratio of adjusted rent to aggregate disposable income which existed at the time of approval of such head of the household's last application for a rent exemption order or for renewal thereof; provided, however, that in no event shall the amount of adjusted rent be redetermined to be (i) in the case of a head of the household who does not receive a monthly allowance for shelter pursuant to the social services law, less than one-third of the aggregate disposable income unless such head of the household has been granted a rent exemption order that is in effect as of January first, two thousand fifteen or takes effect on or before July first, two thousand fifteen; or (ii) in the case of a head of the household who receives a monthly allowance for shelter pursuant to such law, less than the maximum allowance for shelter which such head of the household is entitled to receive pursuant to the social services law. For purposes of this paragraph, a decrease in aggregate disposable income shall not include any decrease in such income resulting from the manner in which such income is calculated pursuant to any amendment to paragraph c of subdivision one of section four hundred