I have seen some mention of removing the OEM secondary narrowband sensor and populating that bung with a replacement WB AFR sensor. I am somewhat concerned with the accuracy of post-cat readings and the effects of removing the second O2 sensor from the ECU. Is there a way to remove this map from the factory tune, or is it a better idea to add an additional bung adjacent to the pre-cat sensor? I have purchased the AEM unit.

 

This is a bad idea, and instead you should buy a header that can accommodate a WBO2 sensor.

Contrary to forum anecdotes, having the WBO2 post-cat (functional) is not a big deal and might cause a 0.2 variance in AFR (in the lean direction).
The issue here removing the rear O2 completely. I mean, in 2021 there might be some tuning that can be done to eliminate that ECU Fault, but it's a bit cheesy if you ask me.