[Haskell-cafe] "desactivate" my Show instance implementations temporarily

Hello, I have a module where I have made several types as instances of the Show typeclass. For debugging purpose, I would like to use the default implementation for Show (the one obtained when using "deriving", which shows all the constructors). Is there some option to do that, or have I to comment all the Show instances of my code, and add "Show" in "deriving (...)" for each of my types? If this is the only possibility, is there some script around here to do that automatically? Thanks in advance, TP