Modifying the kernel's make install initrd image

# Login as root
# mkdir myinitrd
# cd myinitrd
# gzip -dc < /boot/initrd-your-version-here.img | cpio -i
# edit init do what you want at the top of the script. Usually custom scripts added after mounting /proc but before mounting any drives
# find . | cpio -o -c |gzip -9 > /boot/initrd-your-version-here.img