Heyo,
In the rules it says that Rifles embody any and all 'long arm' - assault rifles, battle rifles, and submachine guns - and that when using a Retaliator that you must have both the stock and barrel extension attached in order for it to be considered a Rifle. This makes sense, especially when considering that a stripped down Retaliator can be used as a pistol.
My question is this - can I modify/use a homemade barrel extension to shorten the length of the barrel, making it look more like a submachine gun? There wouldn't be any modifications to the internals, jut a purely cosmetic change for in-game purposes.