Section 161. Period for which rent is not liable to modification

161. Period for which rent is not liable to modification.— Save as provided in section 163, when the rent of an occupancy, an exproprietary or a hereditary tenant has been commuted, abated or enhanced in accordance with the provisions of this Act, it shall not be liable to be commuted, abated or enhanced unless — (i) in case of abatement or enhancement of rent — (a) the revenue payable by the landlord has been revised; or (b) there has occurred a decrease or increase in the productive power or the area of the land held by the tenant, as provided in clauses (b) and (c) of sections 153 and 154; or - (c) the sanctioned rates have been altered; and (ii) in case of commutation of rent, a period of three years, or such longer period as may have been extended under section 83, has elapsed since the date of the last commutation order.