How to disable RIL on Android?
The consequences of disabling the RIL daemon (rild) is hardware dependent. Because RIL is getting more and more involved in all aspects of Radio related items, including WiFi. The easiest way to stop RIL is by killing rild. But you need to have a rooted device to do this. Open a command shell and get root prompt (#). 

# kill -9 `pidof rild`


You can then check the current status with:

# getprop |grep init.svc.ril
...
[init.svc.ril-daemon]: [stopped]
[init.svc.ril-qmi]: [stopped]


To restart rild you have to point it to the right device and library files. You can find what these are with:

# getprop | grep rild.lib
...
[rild.libargs]: [-d /dev/smd0]
[rild.libpath]: [/system/lib/libril-qc-qmi-1.so]


Then restart with*:

# rild -l /system/lib/libril-qc-qmi-1.so -- -d /dev/smd0 


* PS. I haven't actually tried this line, so feel free to edit this post. It's possible you also need to supply the correct SE context to SU as well...