Seems like customized commanders are not available in single player modes like missions or skirmish. I understand this is probably not a big priority for the devs, but it would be nice for beginning players to have a safer game mode where to test loadouts.
-Edit: I actually meant the preconfigured commanders that players can customize themselves. The commander morphing ingame from trainers is alright, but if you are trying to make good loadouts for fast morphing in PvP etc. it would be nicer to get to try your own preselections in skirmishes and so on.