I understand now, you mean that “fly again” while being a guest of a mission that you are not allowed to play because of tiers or environments (not because of CHL) will make them the host, allowing them to temporarily access the mission as the host until they leave the results screen.
If you are allowed to fly all missions normally as guests (but not hosts) regardless of environments and tiers, to prevent exploiting like above (“fly again” to become a host of a mission that you are only allowed to play as a guest), I think disabling the “Fly again” button should suffice (originally reported above).