Generally, you are not allowed to change plans between enrollment periods if your health condition changes. You can request an exception to the plan’s formulary, but even if it is denied, you are still locked into your plan until the next annual ACEP enrollment period. None of the money you spend on the non-covered drugs counts toward your out-of-pocket limit.
On the other hand, if you are receiving Medicaid or are living in a long-term care facility, you can switch plans at any time.