Replacing vinyls in "Need for Speed™ SHIFT"
So, to get to work we will need:
1. A collection of programs called "BFF Tools". You can download it here.
2. The photo editor "Paint.Net" (you can download it here) or "Adobe Fhotoshop CS3 with the .dds plugin" (you can download the plugin here, and the photo editor itself here).
Next, open the file "BffUnpacker.exe" in the archive. Open the last folder by following this path: Need for Speed - ShiftPakfilesVehicles (the 3 asterisks are your local drive and other folders, if any). You select the cars. For example, you chose the Subaru Impreza WRX STI 2009. In the path "Need for Speed - ShiftPakfilesVehicles" each car has 2 files: one ends with just ".bff", and the other ends with "Cockpit.bff". You select the one that ends with just ".bff". Then scroll down and find the files whose names end with "livery0*.dds" (the asterisk may be the number "1", "2", "3" or "4"). Select one of the four textures, right-click it and choose "Extract selected file(s)...".
Create a folder and save the texture into it. Next, using one of the two photo editors, open this texture and edit it however you like. Then replace it with the one you edited, saving in .dds format. Then run the file "BffInject.exe" in the archive. Where it says "Source Folder", select the folder you created when exporting the texture. Select the folder you created, not the texture. Click "OK". Where it says "BFF Archive", select the car's file (i.e., for example, if you are making a vinyl for the "Subaru Impreza WRX STI 2009", then you must select "SubaruImprezaSTi.bff"). Click "Inject now", wait, and that's it! Done!
Now you need to enter the game, buy the car you made the vinyl for, go into "GRAPHICSAPPLICATIONS" and choose the paint job.
Example:

Enjoy the game!