When Mandrakesoft became Mandriva I did not want to change manually all my contacts, so I wrote a small ruby script to do it. It's really short and trivial but it could be usefull to some other people, so here it is. Even if you never used ruby, you'll find out easily how to change something else :-)
Warning: Please check that all you data is still there after running it, and restore the .bak files if there are problems. If you run it another time, you'll lose the original data.