More than likely. You probably slapped the fuel around enough for it to think the cap was off (surprising it didn't do it earlier). This is a "feature" of OBD2.
I haven't checked it, but more than likely. All you needed to do was remove the CLOCK/RADIO fuse from the under-hood box. This removes the backup power from the ECU (as well as the radio, have your code handy). Could have just been a time-out or the ECU self-resetting.
Shouldn't, though the ECU will correct eventually for the cams with ignition timing and fuel trim. You'll need to reset the ECU every few days or put a switch on the backup power line if you want to stop this. I'm not sure what pulley settings make what power, but I know the ECU is smart enough to adjust what it can to compensate for the altered emissions.
All ECU errors generate the Check Engine light. ATTS has it's own, the brake system has it's own, the ABS system... any engine or emissions related problem pops the Check Engine light.
