You may elect to change plans during Annual Enrollment prior to becoming Medicare eligible OR you may stay enrolled in the Consumer-driven Health Plan. Becoming entitled to Medicare allows you to cancel coverage completely if desired but does not allow the ability to change to a different plan (i.e., Premier PPO). If you decide to cancel due to becoming Medicare eligible, once you enroll in Medicare you should notify your ABC within 60 days that you want to cancel your medical coverage through the state-sponsored plan completely by submitting a cancel request form. The cancel request form can be found here: 1048_2020.pdf (tn.gov). You may not provide the maximum IRS-approved HSA contribution to your HSA since you will not have HSA-approved coverage the full 12 months of the year.
The maximum HSA contribution amounts can be found on the Partners for Health CDHP/HSA webpage.