How about "special weapon" called Camouflage , it would replace your main gun (considering that in future updates there will be secondary pistol) and change your color for enemies. Due to lack of "main firepower" you'll have to stick to your knife and maybe collectible silent pistol to assassinate people.

How it could work:
- You get a camo item, you get some random 1st ranked soldier disguise.
- When you get a kill, your camo disappears for like 2 seconds, so if you kill someone in the middle of the group, you're screwed.
- After two seconds (if not spotted) you're disguising as the person from your last kill.
- It could lead to other opportunities, like if you're disguised as general then enemy soldiers will start to follow you.
- Command your full squadron to fame aka. CHARGE THAT FULLY FORCED AND SUPPLIED BUNKER, FULL OF TANKS! FOR GLORY! etc.
- When an enemy player is 5 meters from the spy and places his cursor over him, he sees his true form.
What do you think?

Like in Team Fortress 2?
I'd prefer if it was like Hitman, where you could kill someone, swap clothes and hide their body.

It would be hard to hide a body that disappears after several seconds