I think it'll be a lot of work. Not persť the modelling, but you'll have to re-UVWmap the model fully. So that your new mesh gets decently mapped.
Then it's the question on how the animation part of the model will react to the new piece of mesh.
I know SithSpecter altered the Revan model to include animation for the cape; by adding extra bones. So perhaps alterting the mesh and then adding the correct animations back into the model might give you an updated droid model. But be prepared to fix certain animations. I guess the droids have less animations then the player 'human' characters, but it's still a big chunck; so to speak.
For the technical side I'dd contact Sithspecter about it. I never messed around much with the NPC characters and such.
Lot of work though