Can I copy the Atahualpa folder to proof it against accidental upgrades?

I've just had a client update everything on his WordPress including the theme, which wiped out a lot of the work I had done.

When I build a site for someone I often make them video tutorials using their sites so I'd rather they keep the old version of Atahualpa, otherwise it's going to look different on the tutorial.

So, to safeguard against someone doing this again, is it possible for me to copy the entire Atahualpa folder, rename it and put it back in the Themes folder?

Then could I either set that as the theme in use or keep it as a backup?

Sorry if this is already on the forum, I did search but have a head full of flu and no brain cells.
Lisa