Cargolux doesn't have SO's or cruise pilots. Everyone is being hired as FO (junior). Depending how you agree within the crew, you’ll be flying FO or operate as a relief pilot on that very sector. Sometimes even you fly with two captains, then one of them work as a relief pilot.
Cargolux is very easy going in that sense. It is not much of the hierarchy as in, for example, many Asian airlines like Cathay.