All the high alt CPS is advance engine timing which at lower altitudes gives you more power. If your knock sensor is working the computer will retard the timing until no knocking occurs.
I would think it would lead to better emissions since the fuel is burned at the compression ratio just on the verge of knock.
I do not have to do emissions but at 125,000 miles replaced the cat converter, that sure helped the back pressure problem and finally solved my oil in the air cleaner problem.
I would not worry about it, just do all those tricks everyone talks about before you take it in. You know, take the vehicle for a 30-45 minute drive before you show up at the test station.
I think you will do fine, I never had my XJ tested since it was never registered in a county that needed emissions testing.
