I've just added Atahualpa 3.4.2 as a theme in my test environment when a thought occurred to me. What happens when it's time to upgrade? Can I change the folder name to atahualpa3 and hope for the best?
testblog-->themes-->atahualpa342

If you name the theme folder with the version number (i.e.atahualpa333, atahulapa 340, atahulapa342) you can have as many copies in your theme folder as you like AND you can switch between them (I do this testing things all the time)

thanks
I changed the name to atahualpa3, with no ill effects, so all is golden