what if I change my pipes?? What would I need to do to just make them open pipes? I need this bike to have a meaner sound.
If you're asking if you need to retune it; probably not as long as you have a stock type air filter.
The issue of a lean air fuel ratio comes up when you have a freer flowing intake and exhaust. Since the engine is actually running more like what it was designed to and not what the EPA mandated; you need to richen up the mixture with one of the many tuners available.
Your 07 is before they made the change in 08 so one of the basic dobek style tuners will work fine. Like I said though; if your intake/air filter is stock you likely won't have to do anything but heck; you might as well get a K&N filter and a tuner at some point just so your bike has more umph.
My 04 has pretty much the same engine, just has less cubic inches, and it just has the stage 1 exhaust mufflers on it bolted up to the stock header pipes. Runs great and I love the sound. Can't buy those exact ones anymore but there are others out there that sound good too.
You can drill the holes to get more decibels out of the mufflers but it will be up to you to decide if that's the tone and sound you're looking for. I don't care for it personally but it's a really subjective thing. If you're looking for a deeper and throatier sound you will need different mufflers. Careful though because some are really loud.
So when I read this correct the stock pipes stay bolted to the engine, then you remove the really heavy stock muffler part and replace that with a open pipe?
Yes, you replace the mufflers only and leave the stock head pipes. On a steel frame bike it's probably good to bore out the catalytic converters (catastrophic diverters) too. They are right at the end of the head pipes.