Even though I have never been to the Hilltop facility, it seems to me like this is not something they do. And I find this easy to understand.
The AFR needs to be recorded before the exhaust reaches the cat. The cat. is part of the header pipes. The cat also blocks for putting in a probe past the cat. Just putting a probe into the exhaust will give a AFR reading, but the reading will be of no value as the exhaust by then has passed through the cat, and the values have changed towards a way leaner reading.
You may replace the O2 sensor with a wideband sensor, but then the ECU gets no feedback and starts running in a Limp - mode.
It would be possible to measure the AFR if you replace the O2 with a wideband sensor, and then you program an adapter that will extract info from the wideband sensor and provide the ECU with the modified data, sort of like what the AF-XIED do. I don't think Hilltopp uses an AF-XIED...
However, if the header has been replaced with a no-cat header, the reading will be more correct.
Anyway. Good luck with the HT job.