I don't believe you can change a file on a even a CD-RW without rewriting the entire ISO. If you know software that can edit an ISO without having to extract all the files and make a new ISO, I'd really appreciate it.
When you burn an ISO to a cd, it extracts the files from the ISO. So if you look at the files on the cd after you burn the ISO to it, those are the files that are in the ISO and (if it is a CD-RW) you should be able to edit the files on there. About editing an ISO, if you have not burned the ISO to a cd yet and you want to change a file, you can mount the ISO into the /mnt/loop folder by entering this command as root in a terminal:
mount -o loop /path/to/ISO /mnt/loop
After entering this command, you can go to the /mnt/loop folder in your file manager and see and edit all the files from the ISO. You can also just look at the files in an ISO by opening a terminal and typing mc. The mc file manager will start and then you can navigate to the ISO and mount and enter it by clicking on it just like you would to go into a folder. You can even use one of these methods to copy the contents of the ISO onto a cd instead of using a burning program. (I think the mount command is easier for this.)