The current store() methods unconditionally add comments and timestamps. It would be useful to have an overload or another method that writes the properties without adding any comments. This could be as simple as

    void store(Writer writer)

This would allow the caller to write additional information before or after the call. The properties would be written in String sorted order (which is not locale specific). The line terminators used will need to be determined. Also consider returning the Properties instance to facilitate chaining.