The drainage board for an internal drainage district may at any time make such amendments in the current or last preceding drainage rate as appear to them necessary in order to make the rate conform with this Part and, in particular, may—
correct any clerical or arithmetical error;
correct any erroneous insertions or omissions or any misdescriptions;
make such additions or corrections as appear to the board to be necessary by reason of—
any change in the occupation of any hereditament; or
any property previously rated as a single hereditament becoming liable to be rated in parts.
The drainage board for an internal drainage district shall serve notice of any amendment made by them in pursuance of this section on the occupier of every hereditament affected by it.
Where an amendment is made in pursuance of this section—
any amount overpaid shall be repaid or allowed; and
any amount underpaid may be recovered as if it were arrears of the rate.