If I want to re-do part of a campaign mission for an Achievement, do I lose all the missions that I have already played through (as like a reset)? I just saved at the very beginning of the 6th mission, so I have literally done nothing in terms of checkpoints for that mission. I want to get the Diggin’ Up the Past achievement from Dawn mission since I missed it originally, but I don’t want to have to restart the entire campaign from that point.