Quick search by citation:

5 U.S. Code § 8465 - Waiver, allotment, and assignment of benefits

(a)
An individual entitled to an annuity payable from the Fund may decline to accept all or any part of the amount of the annuity by a waiver signed and filed with the Office. The waiver may be revoked in writing at any time. Payment of the annuity waived may not be made for the period during which the waiver is in effect.
(b)
An individual entitled to an annuity payable from the Fund may make allotments or assignments of amounts from the annuity for such purposes as the Office considers appropriate.