1. If the existing converter is not plugged, a new pipe can be fit to that to connect to the muffler. In that case, the rear (secondary) OČ sensor can remain in place.
2. If the cat is replaced with straight pipe, a simulator for the rear OČ sensor can be installed in place of the original zirconia sensor to "fool" the PCM into thinking it has signal and not set an error code.
This is not an endorsement, just an example of what that is and how it works:
https://www.afterthoughtsauto.com/o2sim.html
You can also construct your own if you like:
https://www.youtube.com/watch?v=qHD7T7EhuzI
Of course, the primary sensor will need to be left in place in order to maintain proper mixture control, regardless of what the convert is doing (or if it even exists).
These methods can be used to test whether a rear sensor error is due to a converter problem or wiring fault. The duration of the "test" is completely up to you.