It is possible for rebels to flag themselves Imperial in Deep Space and Kessel.
Need:
Rebel Pilot(Did it as Arkon's Havoc)
Ability to fly a JSF
Launch in your JSF. Fly to the rebel space station, the one that is the rebel entrance to Deep Space/Kessel in the Dantooine System.
Launch into either Deep Space or Kessel. You will hyper into the system and be declared an Overt Imperial Pilot, allowing you to attack the Rebel Space Station, the Rebel Corvettes(Easy way to get xp for the last 3 boxes), Rebel Gunboats, and Rebel Starfighters.
This has been done after Ch. 4 has been released.
EDIT::
Just did it again as Crimson Phoenix Squadron. Took a SS. View it here.
http://i63.photobucket.com/albums/h149/ ... pasReb.jpg
EDIT::
Spelling
EDIT for response to extacee(as I can't reply):
Can look at it a couple ways. It is an exploit. You arn't supposed to be able to flag yourself at the oppisite faction. Besides that, it allows one to slip behind enemy line and essentially spy if your having a PvP battle, or one that is really helpful when grinding the last boxes, is that you can kill Rebel Corvettes for 43,000 x Experince Modifier. Since Corvettes really arn't that hard to kill after you've got some experience on them, thats a really fast way to get your experience.