Maby haha Im also wondering will it mess with the engine because the o2 senceor will think the cars runing to rich and try to lean it out?

 

the o2 sensor is before the cat, so no.

 

Just to clarify:

The front O2 censor is before the cat so it won't see a difference. It is the one the actually has anything to do with what the ECU does with the tune.

The rear O2 censor is after the cat (well in the middle of ours), but does nothing besides checking emissions. It will throw a code (fix mentioned above) but has no say in how the car runs.