17.—(1) Subject to sub-paragraph (2), where a court proposes to exercise its powers under this Part, otherwise than on the application of the offender, the court—
(a)shall summon him to appear before the court; and
(b)if he does not appear in answer to the summons, may issue a warrant for his arrest;
and the court shall not amend a relevant order under this Part unless the offender expresses his willingness to comply with the requirements of the order as amended.
(2) This paragraph shall not apply to an order cancelling a requirement of a relevant order or reducing the period of any requirement, or substituting a new petty sessions district or a new place for the one specified in the relevant order.