You could drill the stock exhaust out, but the release of the extra backpressure would still need a retune.
And honestly, you'll save a LOT of weight by getting different pipes. Less weight = better performance.
Now, when you go to select new pipes, remember that most all pipes available are small diameter pipes, so you won't get a deep, rumbling sound. The ones that do give you that deep, rich sound will be the RPW Big Slash, Hardkrome Sideburner, and the Conquest Customs Octanes (Octanes not quite as deep as the others, but much louder and impressive IMO).
Also, the shorter the pipes, the louder they will be. The Arlen Ness Slashness pipes are considerably longer than the RPW Slash or Santa Rosa pipes, so while they look the same, the longer length make the Slashness quieter. I have the RPW Slash pipes and they are loud, plus they sound great.
If I had it to do all over again, I would only buy the Conquest Customs Octanes or Ground Pounders. Not only do they look mean as hell, sound mean as hell but they are wrapped pipes. I've found that most all aftermarket pipes for our bikes tend to stick out in a way that it's really easy to hit or rest your leg on them. My black Slash pipes have permanent marks on them in 2 spots... one spot from my jeans flapping against them while riding, and another spot where my jeans touch them when my feet are down.
At stoplights, i have to extend my right leg out a bit to avoid the radiant heat... wrapped pipes throw off a LOT less heat.