First you've got to extract the dat with CMagic but for that, and IT'S IMPORTANT, DONT USE THE PATCH BUT THE ORIGINAL EXE, otherwise you'll allways have the error message and you'll never be able to edit the file. After, replace the exe patch, open the file made by Cmagic and change the fuel values.
Each time you'll edit a magic file YET EXTRACTED, use the patch. You'll allways have too an error message, but don't worry and carry on cause it's normal.
Vous avez voulu Hollande et les socialistes, vous les avez !!! Au secours, la France est au plus mal !