^^A tune or a cheat, yes. Depending on what county You're registered in will depend on whether or not You have emissions testing. Here in Travis County it's a simple OBDII test, no emissions, so a header is a non issue.
Oh, and I hate to go all pronunciation nazi, but it is "header" not "headers", as headers are multiple exhaust manifolds(found on v type engines) whereas We only have the one, making it a header. Sorry, pet peeve of Mine. Carry on.