Putting it simply - you cant modify your car.
If u want to take the risk, you have to be a bit smarter and have a little more $$ (you may have to remove these mods for yearly passing).
For instance, if u want to modify ur engine with the basic intake and exhaust - dont get the loudest exhaust, with a 4 inch muffler and drive at WOT all day... ur going to get caught.
The general idea should be to get your car looking & sounding as stock as possible. Then there is a good chance that you wont get pulled over & that ur car will pass each year.