If getting pulled over is what worries you, unless your car is spewing smoke or flame out of the back, technically in CA, what you need to worry about（reason for cops to pull you over) is actually noise. The CARB regulations (pollution) are enforced at the time of smog check.
Relevant V.C.
V C Section 27151 Modification of Exhaust Systems
V C Section 27153 Exhaust Products