hey man, play it safe, read that sticker carefully, if it's what i'm thinking it is (about 1inch x 2inches white with black letters) it's a state ref ONLY sticker, no officer writeoff. if that's the case, then the cops you went to are probably trying to be dicks to you. take off your downpipe, put the stock one back on, replace your old exhaust back on your car, then go to the ref. have him sign that everything is ok, then be done with it. put your exhaust stuff back on later after you've cleared it. do NOT let this balloon up. you can get in some serious trouble if you try to "get away" with things, even if they are legal... see, the thing is, even though your exhaust may be legal (if it is), the dp isnt, and no blow off valve is legal either, also, your intake may not be legal, etc etc. list goes on. just replace the exhaust and avoid trouble.

i had the same thing happen to me, but i wanted to "get away" with a legal db level exhaust, but see, i have an illegal engine, so to avoid the matter entirely later on after i had already dug myself a hole, i paid nearly $1000 in fines so as to clear my record.

play it safe man, not all cops are bad, but it just takes 1 that wants to dick you to... well, really dick you.