5 USC 3347 – Exclusivity
(a) Sections 3345 and 3346 are the exclusive means for temporarily authorizing an acting official to perform the functions and duties of any office of an Executive agency (including the Executive Office of the President, and other than the Government Accountability Office) for which appointment is required to be made by the President, by and with the advice and consent of the Senate, unless—
(1) a statutory provision expressly—
(A) authorizes the President, a court, or the head of an Executive department, to designate an officer or employee to perform the functions and duties of a specified office temporarily in an acting capacity; or
(B) designates an officer or employee to perform the functions and duties of a specified office temporarily in an acting capacity; or
(2) the President makes an appointment to fill a vacancy in such office during the recess of the Senate pursuant to clause 3 of section 2 of Article II of the United States Constitution.
(b) Any statutory provision providing general authority to the head of an Executive agency (including the Executive Office of the President, and other than the Government Accountability Office) to delegate duties statutorily vested in that agency head to, or to reassign duties among, officers or employees of such Executive agency, is not a statutory provision to which subsection (a)(1) applies.