Not sure what rule you are referring to that says a title can't ever be edited. Actually a thread can be edited up to 30 days from the thread start date by thread starter them self, after that it's locked for archiving. A thread starter may however still request a thread title edit or the thread to be buried once it passes that 30 day date. ONLY a thread starter may request a thread be altered (for obvious reasons).
I would suggest getting in touch with the thread starter to see if they will either edit the title for you or if they will report their thread so staff can do it for you.
Hope that helps,
Eric Lyon