I live in MA, have a blower on my 88 Stang, no problems what so ever. Cops around here only care about noise pollution and speeding...although either of those two things alone applies to almost every mustang. Better keep your license and registration out , throw on the dome light keep your hands on your steering wheel and give him the old- what seems to be the problem officer?- works everytime. Once in a while you run into a cop with gasoline in his blood and he just wants to see what you have under the hood you get off with a verbal/written warning.One thing is for sure- dont get caught without any cats visually underneath the car. If you must hollow them out from the topsides. Good Luck
As far as the blower... dont worry about it- as long as its a CARB approved designated kit. As soon as you change the pulley it becomes "illegal" in most applications- however- the only way someone could actually tell is when your car does not pass emissions.