With reference to Why didn't Han know how to talk with the guard Captain when attempting rescue? which I consider to be a fail.
In Legends, Han was a former Imperial soldier (idr him being an officer but he was definitely an Imperial before busting Chewbacca out). Has there ever been an instance of him successfully posing as an Imperial soldier in Legends?
Yes, and with a great deal of success. In the "Truce at Bakura Sourcebook" we learn that shortly after destroying the Death Star, Han and the Endor Strike team went on a vital mission against the Star Destroyer 'The Accuser'.
Dressed in a General's uniform and with a squad of disguised rebels he ordered the evacuation of the ship's original crew and took control of the vessel.
Ackbar: Preposterous. Surely you are exaggerating, Lieutenant.
Page: No,sir. After all, we did have the proper Imperial clearance - the code that allowed us through the shield perimeter at Endor - and General Solo was quite convincing when he called the Accuser's captain claiming we had just escaped from the Death Star. They certainly fell for it; they actually used their own docking tractor beams to bring us in.
Mothma: They brought you in?
Page: (Smiles slyly.) Yes ma'am. You could say they invited us aboard.
Ackbar: And how did you eliminate the crew?
Page: Er, General Solo actually managed it.
Mothma: Of course he did.
Page: Once we took the bridge ... and, I swear all we did was just walk in ... he uh, relieved the Accuser's captain.
Ackbar: Let me see if I've understood you correctly, Lieutenant. General Solo - posing as a stormtrooper - boarded an Imperial Star Destroyer, marched you and your group to the bridge and assumed command?
Page: No, sir. General Solo was wearing an Imperial general's uniform, not stormtrooper armor.
Mothma: (Chuckles softly.) A general. Naturally.
Solo: Hey, it fit, that's all!
Ackbar: And how did you and your team manage to eliminate the Accuser's crew?
Page: General Solo convinced them to leave.
Mothma: convinced them ...
Ackbar: to leave ...
Page: Er, well, he rendered the Star Destroyer's captain unconscious while my people secured the rest ofthe bridge crew. Then the General activated the ship-wide hull breach alarm and ordered the crew to, er ...
Ackbar: To abandon ship.
Mothma: (Shakes head.) Amazing.
Solo: Oh, knock it off. It worked.
