How to use the permanent unlock token

I just discovered a post on reddit in which a user used his token to unlock "Ghost" permanently, then selected the option to reset all stats.

He was downgraded to prestige level 0 again and lost his ghost unlock (among every other unlocked item).

So yeah - don't expect unlocked weapons/perks to remain if you reset all stats.

Source: http://www.reddit.com/r/redditcasual/comments/13cjv5/okay_so_ive_made_a_huge_mistakeresetting_your/

The Knife comes as the default melee weapon and is neither a primary nor secondary. You don't need to equip it, and it takes no slot.

Tactical Knife is a secondary weapon attachment, like a supressor, and replaces your melee attack while equipped. If you switch to your primary, your melee attack will be your regular knife, which is slower.

What you need, though, is basically achieved by NOT equipping a secondary weapon. Then you can run around with the knife, when you switched to secondary, and behold your camo.