they arent illegal, but you have to see what the law says. some states don't allow modified tails, etc, but check it out...
go to
www.sema.org, they should be able to get you the info that states what is not ticketable on your vehicle... intakes/exh, are not and the lights, if they are from a good company, should have a dot (dept of transportation) number on them, which means they are approved/legal. some have a sea number also, more evidence that the cops are profilin.