No further proscriptions or restrictions may be imposed upon employees covered under this regulation except:

(a) Employees who are appointed by the President by and with the advice and consent of the Senate;

(b) Employees who are appointed by the President;

(c) Non-career senior executive service members;

(d) Schedule C employees, 5 CFR 213.3301, 213.3302; and

(e) Any other employees who serve at the pleasure of the President.