Help with replacing a file inside an .iso image?

I'm currently having trouble replacing a .txt file inside an .iso image since it won't let me drag and drop inside it. I've tried going into the .txt file and changing it from inside the .iso but it says unable to save change: read-only file. To be more specific, the .txt file is called "Seen.txt" and used to translate the game "Clannad" which is the .iso image. I've searched the web but all i've found is that you need to replace the .txt file inside the installation folder for windows.