I have been Remastersys to backup my customized distros for what seems like years. Its been a wonderful utility nicely tailored for this task.
But its development stopped few years back, and so there have been couple of alternatives for that.
Just recently I had to put together an ISO of my current OS setup on one of my laptops. So digging around I stumbled upon distroshare utility. This is a nice replacement for Remastersys. Its actually called Distroshare Ubuntu Imager.
After trying it out I found that it does exactly what I was looking for. And I successfully created a Live CD backup using distroshare.