I got a little carried away. Attached below is a Theme Builder bundle, it has one command which generates and switches to a random theme which will target all scopes of the current language (including languages which may be embedded in that).
It does not do anything on my machine?
I had to modified the script at bit to make it work: require 'rubygems'
before the other require's in the script and also install the plist gem (which wasn't installed on my machine) from the shell,
sudo gem install plist
then it worked for me
Martin