I need to edit a text document (some 10k + lines) by finding numerous hexadecimal values and altering them if they greater than a certain value;

e.g. if X > Z then X = X - Y

I pretty sure this could be done with a macro but have had no joy finding an example macro on the net (and I don't want to have to learn Visual Basic as it'll probably be quicker to hand edit the file ).

Does anyone have any idea how to go about this?

Thanks.