I tried to do something similar a few years ago and never got it running. Afaik a resource bundle cannot be easily updated / reread. And you cannot simply extend ResourceBundle and provide your own implementation because most of it's members are private (you'd have to implement it from scratch).
To refresh the contents of a bundle you have to clear the cache (even that wasn't possible before
Java 6!) and reread the bundle:
Of course, for the example to work you have to add '.' (executing directory) to your classpath ; - )