This is an old revision of the document!
Lacks proper editing.
These are the steps to update the system from a snapshot, getting the *.txz.
You have to copy them at /, and extract them directly (you can use tar xfv).
Also, if you want to extract the files from base.txz, you also have to call chflags -R nosunlink,noschg at the files that are to be replaced.
Obviously, I will update this later and get it done in a much better way. For now, this is just a reminder.