((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 , 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 order making such adjustment of status, the Attorney General shall cancel the record of the alien’s admission for permanent residence, and the immigrant status of such alien shall thereby be terminated.
((b)) The adjustment of status required by subsection (a) shall not be applicable in the case of any alien who requests that he be permitted to retain his status as an immigrant and who, in such form as the Attorney General may require, executes and files with the Attorney General a written waiver of all rights, privileges, exemptions, and immunities under any law or any executive order which would otherwise accrue to him because of the acquisition of an occupational status entitling him to a nonimmigrant status under paragraph (15)(A), (E), or (G) of .