In Modern Warfare 3 there is the new Specialist strike package. Basically you choose 3 perks, and you'll be awarded an extra perk every 2 kills. I'm not seeing any way to determine in what order you get these extra perks though. For instance, I might want Extreme Conditioning before I get Slight of Hand. Is it possible to set an order for when you get each of the perks?
The order of the perks granted by Specialist is the order they are selected in. For example, I can set it up so that Assassin is my first extra perk, Extreme Conditioning is my second, and Stalker is my third.
The only restrictions placed on what perks may be selected are the three perks you already have selected outside of Specialist, and perks that you have not yet unlocked.
Just deselect all of them, and then select them in the order you wish for them to be applied when getting kill streaks.