The local housing authority may by resolution—
vary a designation under section 559, but not so as to vary the cut-off date, or
revoke such a designation.
The authority may by a variation of the designation extend the period referred to in section 559(4)(c) (period within which assistance must be applied for) whether or not it has expired.
The variation of revocation of a designation does not affect the operation of the provisions of this Part in relation to a dwelling if, before the variation or revocation comes into operation, the dwelling is a defective dwelling by virtue of the designation in question and application for assistance under this Part has been made.