i think its possible to do this by using a usb stick. i saw a youtube tutorial and after the latest dashboard update you can transfer save games to a usb stick and just edit the file on the stick and then transfer it back onto the hard drive.
i just searched "fifa pro 100%" and it showed the video. defo worth a check if you dont have a cable to connect ur hard drive to your pc...erm..like me! i will try it later today when i get home and report back.