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Sadly the moment you install the update you have no option for going back. Only time Apple is signing two versions is during Beta.
I read this morning, via one of my RSS feeds, of a tutorial that shows you how to return to iOS 6.1.3 or earlier as long as you have those SHSH blobs. Whether or not the tutorial actually works, I don't know and don't plan on trying it personally.
The tutorial can be found HERE.