I am trying to make a easily customizable linux live cd. The user should be able to replace one file in the .ISO file's root folder. I need to be able to read the file after the cd has booted. It may not be embeded in the ramdisk.

Can i pass the file to the kernel via some parameter?
Do i need to mount the cd, what if it booted via usb?
How would i go about doing this?