it's as simple as doing a sed command on an entire directory or Perl if you're into that sort of thing:
sed -e "s/OLDSTRING/NEWSTRING/ig" * should get you there.
perl -p -i -e 's/oldstring/newstring/g' * will do it for Perl
On Windows, make sure you have Sed or Perl
Since we're using Python, doing a recursive regex replace shouldn't be too hard.