Once per year, Medicare recipients have a chance to change their Medicare Advantage policy, and they also have the chance to buy a Medigap insurance policy anytime between October 15 and December 7. But choose carefully. Although Medicare Advantage policy benefits are pretty transparent, switching to a Medicap policy does carry significant risks. In most states, Medigap insurers can turn you down due to preexisting conditions, or charge you more based on your health or age. Don’t cancel your Medicare Advantage policy in favor or a Medigap policy until you fully understand the financial implications.