> I wanted to do something exactly like that some months ago.
> What I ended up doing is using a normal Debian installation
> with an overlay file system mounted over the root.
FWIW, you can do simpler and just use a normal Debian install on
a USB key. That saves the trouble of the overlay filesystem.
And if you want to be able to revert easily to the initial state, then
you can probably get a similar result using an LVM snapshot.
Stefan