With reference to below thread I was able to build ISO with username, hostname and password however I wanted to change issue, issue.net and motd.live.
Wondering how do I do it since I tried mounting squashfs and changing those files and later made sqashfs however I could not succeed. Can someone please guide me?
Yes, you already modify the default config when you build or rebuild ISO, so if you add some commands to the config part, motd and issue files should be changed on the first boot.