Read Thread: Rating Non-Traditional Boxes
I don't believe you can go back. Might be because they don't hold any weight anyway like they do with traditional boxes. Just is there but not functional.
Those ratings aren't used for anything right now so I haven't implemented any way to rate previous non-traditional find. When the day come that it actually does it used for something, I'll provide a way to rate previous finds.
Until then.... I wouldn't worry about it.