Don't worry about the warranty with Axlebacks, I just had an Axleback installed yesterday. I am also in VA, you will pass emissions with an aftermarket Axleback. I have the RTR exhaust. A bit pricey, but it was a Christmas gift. Low deep rumble, some drone around 70, and wakes up when you put the gas down even slightly. Plenty of other great choices, the ones I considered were FR GT500's, Roush, Flowmaster American Thunder, and the RTR's.
2013 GT Premium, Red Candy Metallic, Recaro seats, Electronic package, Strut tower brace, Sway bars, SHR flush mounted window louvers, RTR street-spec axleback exhaust, Ford Racing Boss 302 Side Exhaust, RTR wheels, 50/35% Window tint, Steeda black shorty antenna, and Ford OE Matte Hood Vents.