I needed to reconfigure the hardware UUID of a Linux network adapter caused by cloning a virtual machine. To do this you need to either remove the /etc/udev/rules.d/70-persistent-net.rules and let the system regenerate the file on reboot, or manually edit the file.
I decided to edit the file and manually correct the UUID. I was consistently met "readonly file" so I could not save my changes.
I found using the lsattr /etc/udev/rules.d/70-persistent-net.rules that the file had the i attribute set. This i attribute means that the file is immutable. Removing this attribute using chattr -i /etc/udev/rules.d/70-persistent-net.rules, allowed me to change the file as needed. After editing the file I set the i attribute again using chattr +i /etc/udev/rules.d/70-persistent-net.rules.