I signed up for a stand-alone Part D plan early in the Medicare Annual Enrollment Period (AEP), but then I changed my mind. Can I switch plans if the Medicare Open Enrollment period hasn’t ended

You can submit a new application for a plan other than the one to which you initially applied during the Medicare Open Enrollment period.

Keep in mind that the last plan application you submit before the Medicare Open Enrollment period ends on December 7 is the coverage that will take effect on January 1 of the following year.