Is it set in stone that certain ships have to be used with each faction? For example, the rebellion stole a Lambda-class shuttle in the movies so I would think it would be fun to to let the rebels us use that in certain battles.

Tournament, yes it is set in stone. for some sort of house rules, you can do what you want there and Im sure you could have allot of fun. i think they plan on reinacting the endor scene eventially!

We did one game recently, three way with one person playing Rebels, another Imps, and the third was Fringe; two Bounty Hunters and an Outer Rim Smuggler. But that was obviously a one off house rule scenario.

Rebels with a Lambda; Pirates with Y-wings; Cartels with YT-1300 and Firesprays; etc... lots of scenarios out there covering other factions or borrowed ships.