(a) The status of an alien lawfully admitted for permanent residence shall be adjusted by the Attorney General, under such regulations as he may prescribe, to that of a nonimmigrant under paragraph (15)(A), (E), or (G) of section 1101(a) of this title, if such alien had at the time of admission or subsequently acquires an occupational status which would, if he were seeking admission to the United States, entitle him to a nonimmigrant status under such paragraphs. As of the date of the Attorney General's