Notwithstanding any provision of chapter
83 of title
5, the annuity under subchapter III of such chapter of an officer or employee of the Central Intelligence Agency who retires on or after October 1, 1989, is not designated under section
2013 of this title, and has served abroad as an officer or employee of the Agency on or after January 1, 1987, shall be computed as provided in subsection (b) of this section.