Possible to edit a vehicle from the game?

Is it possible to edit a vehicle from the game and still have it work? For an example if I took the pigeon and extended it. Would I have to remake the jbeam files sense the body has been extended along with other parts? So I did extend a vehicle as a test and saved it as Colada DAE to replace the original DAE. But it didn't change anything in the game. I have looked at the wiki but doesn't give much help when a vehicle that's already in the game.

Any help would be great thank you