This is a Retexture to make the default coop bots look like they have the Pre-order skin. To Access this, download the file and go to your C:\Program Files (x86)\Steam\steamapps\common\Portal 2 location and create a new folder named "portal2_dlc3" or if you've already gotten one change the number to a different number next in line, example: "portal2_dlc4". Then simply drag the pak01_dir.vpk into that new folder. Next load the game. If you haven't installed any vpk before you will have blue dots loading at the bottom left. When these dots turn orange close the game and launch it again. Finally, open the Robot Center and take off any skins you have on and then you're done.
*I* for one appreciate you uploading this. While very simple for anybody to have done themselves, the fact that Valve never kept their promise of making the preorder items tradable (and abandoning/breaking/not-fixing items in general as a whole) still bothers me to this day. People should have easy access to these things when they're told that they'll have access to them.