Hi Gregory,
You could use the m33 application core as you normally would for a "standard M33".
If you e.g. want to run another OS than we provide in NCS you could follow this guide if you want to enable the Bsdlib to be able to easily integrate the communication with the modem.
We do however recommend using NCS with nRF9160 for better support by Nordic and then you also would not need to "reinvent" the wheel when we already have drivers and libraries integrated into our nRF Connect SDK (NCS), and you also get much for free with the Zephyr OS.
If you want to use something else then you can do that, but then you need to integrate that yourself.