To use just the Lora stack you must send the "mac pause" command and then you can use "radio rx 0".
To return to LoraWAN mode you must send "mac resume".
If you are going to use radio rx 0 you can set "radio set wdt 2000" to set the timeout to wait for a rx packet. If you plan to do continuous reception you should set "radio set wdt 0".
I've test it and works fine. Remember that if you are using LoraWAN in (adr) Adaptive Data Rate the radio will retain the last channel settings,