In the case of a waiver of a provision of part A of subchapter IV in effect with respect to a State as of July 16, 1996, or which is submitted to the Secretary before August 22, 1996, and approved by the Secretary on or before July 1, 1997, if the waiver affects eligibility of individuals for medical assistance under this subchapter, such waiver may (but need not) continue to be applied, at the option of the State, in relation to this subchapter after the date the waiver would otherwise expire.