| depends really, what exactly is it that you want to do? most people here will be able to answer your q's on whats legal and whats not, you can jus ask around, and believe it or not, cops are a great source of info for this as well
basically, most anything you do to your car is illegal, haha, its only a question of enforcement, like take my car for instance:
-front license plate: mandatory to have it displayed on the front tag-holder, not the windshield, i have none at all, illegal hehe
-hyperwhite headlight bulbs: higher than standard wattage, thus illegal
-hyperwhite signals: must be amber, therefore these are also illegal
-tints: i live in maryland, which states 35% all around is maximum legal, mine are 20%, illegal again hehe
-exhaust: supposedly, you cant have an aftermarket exhaust thats louder than a certain amount of decibels, im not sure what, mine's deep but loud, so it tends to sound quieter than it really is if you measure it with a sound meter, so that might be illegal
i've been pulled over with these mods once (speeding) and got no trouble.. where i live, montgomery county, cops are extremely lenient on those mods, tonsa people here have modded cars so its rare that they'll ticket you for them.... if you act like an a$$ to the cop, or you're REALLY breaking the law (i.e. swerving or aggressive driving) then they'll tack it on, but they wont pull you over JUST for having the stuff (as quoted by a RCP officer i talked to about tints, hehe) | 
