Short answer: Usually only at renewal or after a qualifying life event. Mid-year plan swaps are generally restricted, and changing plans can reset deductibles and out-of-pocket totals.
Most carriers lock plan selections for the plan year, so an employee typically can’t move between plan options until the next open enrollment; unless a qualifying life event (marriage, birth, loss of other coverage) opens a special enrollment window. Even when a mid-year change is allowed, switching plans often resets the deductible and out-of-pocket accumulators. Employers should set expectations that plan choices are generally annual.
Sources
26 CFR 1.125-4(a) — a Section 125 cafeteria-plan election may be revoked and changed mid-year only as provided in the regulation, so plan elections are otherwise locked for the plan yearecfr.gov/current/title-26/chapter-I/subchapter-A/part-1/subject-group-ECFRb467872627553f1/section-1.125-426 CFR 1.125-4(c) — change-in-status events permit a mid-year election change consistent with the eventecfr.gov/current/title-26/chapter-I/subchapter-A/part-1/subject-group-ECFRb467872627553f1/section-1.125-4