modifying flows
 

I just put a set of 2 chamber flows on my 91 5.0 about two weeks ago. Up untill yesterday, I had them running with turn downs untill I got my tailpipes in the mail, and they sounded awesome. I put my tailpipes on yesterday and my car became so much quieter it wasn't even worth all the time and money I spent putting my exhaust on. I want to go back to turndowns but I would also like to be able to have my tailpipes on it because 1. Maryland law requires tailpipes, but mainly 2. the noise can get annoying after long highway driving. So I would like to follow the barrell cap idea I read about which involves welding barrell caps onto the flowmaster mufflers next to the exhaust outlet so I can choose to put the cap on or take it off. Except, I want turn downs welded onto the flows and then weld the barrel cap to the end of that.
My question is, I know flowmasters use resonance noise canceling techniques, so will the added volume from the turn down effect the sound of the flowmaster when using the tailpipes, or even when using the turndown itself?

I know you can use the barrel cap on most mufflers because alot are "turbo" type with S-curved baffles but the flowmaster would probably sound different because the resonance would be changed because you'd have two outlets. If you cut into the muffler you may even be cutting into one of the baffling walls. I personally wouldn't do it. If i were you, i'd get an offroad h-pipe, which is pretty easy to swap when you feel like it. A guy in my school has two chambers with an offroad and it is LOUD and sounds pretty cool even with full tailpipes.
Good luck on whatever you choose.