Unfortunately just changing the hex value for your current amount of Gil won't work. Just trying this in a hex editor, saving it, and then trying to load your save point in FF7 will result in the error "Data is ruined." popping up when you try to play it, and this is true for any value. Take a look in a save file and try editing a name (for example, look for "LOUD" which is the tail-end of Cloud's name in FF7 text format, and try changing the O to a P, say). This is because there's a checksum in there to make sure save data isn't damaged/tampered with/whatever, so if you want to edit the data in the save file you have to edit the checksum to match the data in the save file. Now I've no idea how Qhimm managed it but if you look at his source code (cheating, I know) he's got a function in there that recalculates the checksum based on the updated, edited values and writes it to the correct area in the save file so that there are no problems when it comes to loading the save file in the game. Or if you don't want to look at it, perhaps you could ask him how he figured that one out.