Yes, as long as you do so during the Open Enrollment period.
People with employer-provided retiree health benefits should know that most early retiree health plans are considered minimum essential coverage, and thus meet an individual’s requirement for coverage.
If you are enrolled in such coverage, you can also look at coverage options through the Marketplace, and if your income is between 100% and 400% of the Federal Poverty Level, you may qualify for premium tax credits. However, there’s one exception. Some employers may provide retired employees with access to an account, called a health reimbursement arrangement (or HRA) that the retiree may use to reimburse medical expenses, including an individual policy through a Marketplace or in the non-group market. A retiree that signs up for an HRA offered by a former employer is considered to have minimum essential coverage from an employer and would therefore would not be eligible to claim a premium tax credit if he or she enrolled in a Marketplace plan.
Remember that outside of Open Enrollment, you cannot voluntarily drop your retiree coverage and replace it with other Marketplace coverage.