As far as I know their is no such tool.
A Repair Install might do what you want and a Clean Install will do what you want. Using a system Restore Point before the problem, (if you are having a problem) would be my starting place.
The reason people ask WHY you want to do this with the registry is a good one.
If we know what kind of problem you are having it will help those with the knowledge of registry repairs to guide you. If you are having problems please state them. If it is just a general question I hope I helped to answer it.