finishing off exhaust

I have a 93 silverado with a 350 The exhaust is by MagnaFLow Performance
The dual exhaust itself extends slightly past the rear wheels angling
out to the side and not the rear but not far enough to the ass end of the truck. The tubes are 2.5" in diameter. Would adding a length of pipe to finish of the line hurt performance any? Change the sound? Or would it be just like adding a tip for looks?
Guy I bought the truck from said to take it to a local garage and get them to install boom tubes on each pipe to finish it off. will give me one hell of a deep rumbling sound but not louder than it is now.
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