These posts always crack me up - If the vehicle is modified after it leaves the factory by anyone (Roush, a dealer, prior owner) the factory warranty is affected up to the point of complete denial of the warranty claim. Read you warranty supplement in your owners manual packet.
I saw a 2 yr old F350 with a Banks 6 gun engine claim get denied when it melted a piston. Banks was installed at another dealer where he bought it - cost ~$16,000
I saw a 7.3 claim get bounced because of a dealer installed K&N filter dusted out the cylinder walls.
A Roush Mustang spit a spark plug (we've all heard of this before) Ford said call Roush, Roush said call Ford... Owner paid out of his own pocket.
I worked at a Roush certified dealer and ROUSH SUCKED to deal with. Ended up charging customers and telling them to go fight it out with Roush.
FWIW, buyer beware!
Adam