This is a bit different then other ISO's. The Ubuntu LiveISO is meant for "checking out" Ubuntu, but they expect you to install it to USB to get persistence, this is not my goal. I want a custom ISO that I can load into RAM that has been modified to suit my needs.
My main purpose for this is to run TeamViewer in a Ubuntu LiveOS in RAM. But that is another long post regarding remote deployment of server with no admin at the other end.
Other LiveOS like Parted Magic are only meant to be run as a LiveISO and therefor have methods for modification built in like placeing apps inside a directory inside the ISO and then the ISO will install/load them.
The Ubuntu method took me a while to figure out a working method, but once it works, all you do is install the program below, make the modifications from inside the OS like you would if it was a real OS and then export a new ISO. (Note: You should then extract the /casper/filesystem.* files and replace them inside the original ISO) I use ISO Master which is available inside most Linux distros.