ACCS should handle the altitude changes pretty well. Some people opt for yanking it off and doing their own jetting, but that assumes a fairly constant level of elevation. I ride anywhere from 4,600-11,000 feet in a day. I'm not going to stop every few thousand feet to fiddle with jetting, so I let my ACCS do its thing. Do I notice differences in performance at different elevations? ...sure, I do... but as long as it runs decent overall, I don't worry about it.
2004 Polaris Trail RMK 136
1997 Ski Doo Summit 500
2000 Arctic Cat ZL550 ESR (in NY)
2000 Arctic Cat 440 Panther (sold)
1980 Arctic Cat Jag 3000 F/C (in NY)
"If it ain't broke, take it apart and find out why!"