what exactly does california emissions mean?
what changes does this make in the engine?
what effect does this have on MPG/HP/Torque output?
how easy is it to change/remove?

not a bonneville, if it matters. i imagine its the same on any CA Emissions car, so i put this in Perf/Brain, but if i was in err, please feel free to move to general chat. its an 06 Mali-Boo.

it means that the car has equipment to make it better for california (which has very strict) emissions testing, this generally is only affected by a more effective, but more restrictive cat, and sometimes an air-pump system.. Genereally Cali-cars will have -5 ish HP

I don't think there is much, if any, difference in emissions controls on new cars. Automakers have come to the conclusion, some time ago, that it is cheaper to manufacture all cars to the same emissions standard, than to manufacture a car line with several different standards. Especially since more states have adopted standards close to California.

And for OBD2 cars, yanking emissions equipment out is a much harder and riskier undertaking.