By gpd You mean a mod right if so you need 3 programs winrar modio and xtaff all can be found here on ttg
first transfer your xbox live profile onto your usb then plug it into the computer use xtaff and keep going deep until you cant go any farther extract that file to your desktop and drag it into modio your account should pop up now click on the unselcted tab beside your name right click inside and click inject choose your file then rehash and resign put the files back in xtaff and then in your xbox voila ill post a vid for you cause thats a little confusing.

unfotunatley this vid uses xport you can also use that but i like xtaff and if you want to give me 3 dollars thats fine

not my video

download winrar google it and get winrar393
after you download it go to gpd file and click on it open withinstald program type in winrar393 and click open it tell the file drag to desktop and open usbxtaf and drag file to usb start up cod 4 and there you go