Can I change Marketplace plans anytime I want to?

In a nutshell, no, you cannot. If you are outside of Marketplace open enrollment, you will need a Special Enrollment Provision, and those include making a permanent move to a new address, having or adopting a baby, recent release from jail or prison, a new marriage, gaining eligible immigration status or a loss of employer group health insurance coverage. Each of these will give you a 60-day window to be able to enroll in a family health insurance plan on the Marketplace.