P0418 is your secondary air pump solenoid.
The p0420 is the o2 after the cat. It just measures the change between the frost and 2nd sensor to make sure the cat is working.
The p0420 has only tripped for me when I removed the cat or the secondary o2 sensor died.
Normally you can use a spark plug non fouler and space it out of the exhaust flow so it won't trip but you have a stock exhaust system. So there is no need to trick the ecu. You need to find out the cause for this.
Is the air pump causing your car to stall? I never dealt with one before
