I'm no expert, but wouldn't the Civic ECU just inject more fuel after it got a "lean" reading from the O2 sensor? I'm pretty sure that's the way they work. If it's a hot day, the ECU will get a reading from the IAT sensor, and with air density to temperature ratios stored in it's memory, the new algorithm will cause the car to inject less fuel. If it's a bigger engine on the Civic's ECU, the O2 sensor will read excess oxygen (Lean Condition) then it will make the mixture more rich by injecting more fuel. The fact that the IAT is reading one thing, but the O2 another may cause the ECU to go into safe mode and worry about the IAT sensor. Besides...lean, not necessarily a good thing. It's not like stock maps run pig-rich, they're only slightly rich for saftey concerns.

My guess is no, it wouldn't work.

I had a member on another forum try this and fail miserably. Granted, he was convinced that changing the ECU would allow him to get higher compression... Yeah, baffles me too.