5 C.F.R. § 894.817
If you and your TEI family members are enrolled in a FEDVIP vision plan while you are retired, and you return to active duty, you will no longer be eligible to enroll in a FEDVIP vision plan and cannot continue to be the enrollee even though you are the sponsor. The current enrollment for you and your TEI family members will terminate and your coverage stops at the end of the pay period for which the premium payment was made from your uniformed services retirement pay. A TEI certifying family member may accept responsibility to self-certify as the enrollee by enrolling and, if appropriate, covering other TEI family members. You are responsible for notifying your covered TEI family members that your enrollment will terminate and of their opportunity to accept responsibility to self-certify as the enrollee. Once the TEI certifying family member enrolls, and covers your TEI family members, they can remain enrolled in a FEDVIP vision plan for the duration of your active duty service. See § 894.601 .
5 C.F.R. § 894.817