How do I create a custom distribution based on Ubuntu 12.04?

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http://askubuntu.com – I am creating the custom operating system using the Ubuntu 12.04. When Ubuntu login from the LightDM -- it shows Ubuntu desktop. I need to change that to my OS name. I need to replace the Ambiance dark icon to fs icon by default for all the login and live CD. How to permanently change the OS name? It should not change even the customer update the operating system too? I am using the remastersys. I am looking to develop the new distro like Mint. If I had a brief explanation of the creation of the repository and maintaining the updates, it will be more helpful. Kindly provide the link for cr (HowTos)