2SSubject to paragraph 6 below, where, on or after 1st April 1993—
(a)lands and heritages included in the valuation roll become or cease to be part residential subjects; or
(b)there is such a change as between the residential and non-residential use of lands and heritages that the apportionments of the net annual value and the rateable value shown in the valuation roll are incorrect,
the assessor shall apportion or, as the case may be, re-apportion the net annual value and the rateable value of those lands and heritages as between the residential and non-residential use made of them, and shall alter the roll by adding an apportionment note to the entry in respect of those lands and heritages or, as the case may be, by deleting or amending the existing note.