...always, always, and without exception, keep a backup of the file you're editing. There's very little you can't do with a hex editor, but there are few better ways of screwing a file up beyond recovery if you get it wrong.Apart from that, it's just a matter of identifying what the critical values in the file mean, and where they are. That's usually a matter of logic with a bit of guesswork and trial and error thrown in. A good converter between hex & decimal is sometimes handy, but learning the 16 times table is better if your mental arithmetic is any good.
