Thanks for all this info Andrii! I spent a while this weekend trying to figure out where they heck the scripts to customize where even coming from.
With regards to Ubuntu 12, I would expect password customization code work fine. I believe there were some big changes with regards to DNS resolution. However, it should work for you if you disable Network Manager which I would recommend anyway, since current implementation doesn't play nicely with it.
I did a minimal virtual server install (use the Ubuntu 12.04 server iso, hit f4 after the first language prompt) which doesn't include Network Manager. I noticed on my 10.04 image that /etc/dhcp3/dhclient.conf was being touched and the equvialant at /etc/dhcp/dhclient.conf on a Ubuntu 12.04 image was not being touched. I fixed this by symlinking /etc/dhcp3 to /etc/dhcp
I have also had success in changing my root password and don't have RPM installed.