“ A person shall be deemed to have waived his rights to reinstatement under the terms of section 528 of the Foreign Service Act of 1946 and the terms of this order if he accepts at the termination of his period of service in the Foreign Service a position elsewhere than in the Government agency in which he has previously served or fails to avail himself of his right to reinstatement within thirty days after the end of his period of service in the Foreign Service. ”