You would need to contact the prospective host and ask them. Each host is different. Generally though, all a managed VPS is is the host will provide 100% support for it as well as maintaining security updates, etc.
If you get root access you should be able to edit configurations, but, again, it depends on the host. So again, you would need to contact whichever host you plan on getting.
If you get root access you should be able to edit configurations, but, again, it depends on the host. So again, you would need to contact whichever host you plan on getting.