Can a person switch carriers outside of open enrollment because they just learned their primary care doctors are not “in network” with their current provider?
The only way to switch carriers outside of ObamaCare's open enrollment period is via a special enrollment period. To switch plans via special enrollment you'll need to have a qualifying life event. Realizing that a service or doctor isn't covered in-network isn't a qualifying life event, typically events are things like moving, losing a job, or getting married, but there are some more obscure qualifying life events to look into.
You can learn all about special enrollment here. If that doesn't work you'll be able to enroll again next open enrollment and start your new plan as soon as January 1st.