Oh I misunderstood your issue,
Yes u can perfectly do that, in several ways more or less good and efficient:
-Exporting your UV map using UVLayout software or something else, but it's tricky, you have to separate each objects composing your model, setting and exporting them to.obj, organize the UV layout .. which can be really long and difficult.. and then being able to texture the UV map in Photoshop ..
More explanations about that

,

and

It's
clearly not worth the effort for some models for conquer in my opinion tho =/ Only use it for some complex highpoly models irrelevant to conquer, that would be a waste of time otherwise
- Using texporter, more info in

from Kutter
- You could just make your own texture, like paint the weapon in photoshop trying to get a similar shape to your model, and then apply the image to the model through material editor in 3DS, and use the UVW unwrap tool to adjust the maps so it perfectly fits the model,
To get the overall shape of your weapon, you could also press F9 in 3DS so you get a quick render of the model, save the image, open it up in photoshop, put a bit of transparency and start painting on another layer maybe ?
I guess there are tons of other ways to do so, best for you would be to google actually, it's not only relevant to conquer so i'm sure you'll find what u need more in depth than here