Cap ship of an fraction and pirating

[Drake]

No capship larger than a gunboat can actually pirate, even if it's part of a pirate faction.

It is theoretically possible to have a lawful capship as part of an unlawful faction (it's happened before), but you'd need a good reason to have it and a good story written. Even if a captain decided to go rogue, that doesn't mean his crew would (extensive crew, on a large ship). And 'I stole it' stories, no matter how well written, won't be accepted.