touched upon in a nearby thread I offer the following:
1. the C's rhs sim check permits pnf operation only. in order to allow pf operation, a rhs line-check (1 sector pf, 1 pnf) is required.
2. the swapping of seats by Cs is not permitted as there has to be one commander for a whole fdp (technically possible if a trg C flew pf lhs out,say, and rhs pnf back but what would be the point?).
3. bmi are far from the only ones doing this: it allows rostering flex when they run out of FOs.
of course, I might have this all wrong but, if I am correct you had better watch out!!!