This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
Class ResourceBundle doesn't have methods to change the values or save its content to a file. But you can read *.properties files with class java.util.Properties instead of class ResourceBundle; class Properties does have methods to change the content and save to a file. Look it up in the API documentation.