(1) When designating an existing provision, the Authority -

(a) must make such modifications to it as appear to the Authority necessary to ensure that, so far as possible, the existing provision has the same effect (subject to any modifications made under sub-paragraph (b)) after commencement as it did immediately before commencement;

(b) may make such modifications to it as have the effect of limiting its application to a class of persons narrower than the class to which it applied immediately before commencement.

(2) The modifications authorised by paragraph (1)(a) include the addition of such transitional provisions as are necessary to ensure the result there mentioned.

(3) If an existing provision designated under article 9 purports to include a modification which is not authorised by this article and which would alter the effect or application of the provision, to the extent that it is not so authorised, the modification is void.