Try This I have got 100% solution and done 99% of customization from here!!
Install pre-requisities
Make sure that you have installed the needed tools
sudo apt-get install squashfs-tools genisoimage
Obtain the base system
Download an official Desktop CD from http://releases.ubuntu.com/
Note: the example shown here uses the ubuntu-9.04-desktop-i386.iso Desktop CD. Replace it with the name of your iso. For example, if you have a ubuntu-11.04-desktop-i386.iso image, the command:
mv ubuntu-9.04-desktop-i386.iso ~/livecdtmp
would be changed to:
mv ubuntu-11.04-desktop-i386.iso ~/livecdtmp
Move or copy it into an empty directory
mkdir ~/livecdtmp
mv ubuntu-9.04-desktop-i386.iso ~/livecdtmp
cd ~/livecdtmp
Extract the CD .iso contents
Mount the Desktop .iso
mkdir mnt
sudo mount -o loop ubuntu-9.04-desktop-i386.iso mnt
Extract .iso contents into dir 'extract-cd'
mkdir extract-cd
sudo rsync --exclude=/casper/filesystem.squashfs -a mnt/ extract-cd
Extract the Desktop system
Extract the SquashFS filesystem
sudo unsquashfs mnt/casper/filesystem.squashfs
sudo mv squashfs-root edit
Prepare and chroot
WARNING: If you do this in 14.04 LTS, you will lose network connectivity (name resolving part of it). /etc/resolv.conf is and should remain a symlink to /run/resolvconf/resolv.conf nowadays. To enable name resolving, temporarily edit that file instead. If you need the network connection within chroot
sudo cp /etc/resolv.conf edit/etc/
NOTE: Recommended that you do not do this unless you know what you're doing Depending on your configuration, you may also need to copy the hosts file
sudo cp /etc/hosts edit/etc/
The remaining steps are good, unlike the ones above:
sudo mount --bind /dev/ edit/dev
sudo chroot edit
mount -t proc none /proc
mount -t sysfs none /sys
mount -t devpts none /dev/pts
(these mount important directories of your host system - if you later decide to delete the edit/ directory, then make sure to unmount before doing so, otherwise your host system will become unusable at least temporarily until reboot)
To avoid locale issues and in order to import GPG keys
export HOME=/root
export LC_ALL=C
Customizations
Apt-get
Prerequisites
In 9.10, before installing or upgrading packages you need to run
dbus-uuidgen > /var/lib/dbus/machine-id
and
dpkg-divert --local --rename --add /sbin/initctl
ln -s /bin/true /sbin/initctl
From here Now you can do all your customization in depth!!
sudo apt-get install --reinstall plymouth-theme*
or any other theme u want to install and save it with
sudo update-initramfs -u