What would happened if I will modify existing ISO codes? Does 'new codes lines" (settings) will automatically apply?

What would happened if change existing codes (gedit files) at USB ISO media or just at ISO file and after dd it to a usb?
Does this settings will automatically apply?

I wanna try that, I read codes from Marmarek developer and wanna implement them to my ISO files.
My, existing ISO codes are fucked up, they missed a lot of codes (compare to Marmarek codes which I show in this thread) I completely understand that I need modify ISO codes for a system can properly work.

Should I modify my ISO image before dd to a usb or Try to modify my ISO straight at usb ?