Wyo. Stat. Ann. § 4-10-403
(b) A beneficiary is definite if the beneficiary can be ascertained now or in the future, subject to W.S. 34-1-139.
(c) A power in a trustee, trust advisor, trust protector or other party designated in the trust instrument to select a beneficiary from an indefinite class is valid. If the power is not exercised within a reasonable time, the power fails and the
property subject to the power passes to the persons who would have taken the property had the power not been conferred.