The Commission, by regulation, may provide for the designation by a merit system employee of the individual to whom the employee’s final salary payment, and any payment due for unused annual leave, should be made on the death of the employee. The designation of the beneficiary shall be: in writing; and on file with the Commission before the death of the employee. The writing need not be in testamentary form. The designation and payment are not testamentary dispositions. The Commission may make the payments described in subsection (a) of this section directly to the beneficiary designated by the employee.