There's only 1 thing I couldn't do to visually finish my mod and it is basically including a new PIC1.PNG and ICON0.PNG inside the ISO. If I do it the file is not corrupted but the patch file is so much bigger, which is not good for players to download. Do you know an easy fix?
EDIT: I solved it myself watching a tutorial. I had to use CDmage which is a program that uses bytes as zeros and helps to not fuck up the ISO.