5 CFR 1651.4: How to change a designation of beneficiary.

(a) Change. To change a designation of beneficiary, the participant must submit to the TSP record keeper a new TSP designation of beneficiary meeting the requirements of § 1651.3 to the TSP record keeper. If the TSP record keeper receives more than one valid designation of beneficiary, it will honor the designation with the latest date signed by the participant. A participant may change a TSP beneficiary at any time, without the knowledge or consent of any person, including his or her spouse.

(b) [Reserved]

(c) Will. A participant cannot use a will to change a TSP designation of beneficiary.