It won't cause a lean or rich code, because those codes are only set by the O2 sensors before the cats. It will set codes from the O2's after the cats though, for "inefficient catalyst" or something of that nature, because the cats are gutted.
If you live in an area that doesn't do smog testing, you can either get MIL eliminators, which take the place of the after cat sensors and stop the check engine light from coming on, or you can have the PCM reflashed, or get an Xcalibrator program that will ignore the secondary O2's.
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