How can I change preferred network type through a script (or terminal command)

Question

I'm currently attempting to create a workaround for a problem that is plaguing a ROM that I'm using. While my phone and ROM are capable of using LTE, and use it perfectly fine, the "preferred network type" dropdown under Mobile Network settings will only allow one to choose 2G or 3G, not LTE. I can change the preferred network to LTE by using the TEST settings, but this is cumbersome, and doesn't stick after a reboot.

My goal is to write a script that will launch at startup and change the preferred network type to "LTE/GSM auto (prl)". Is there a command to do such a task, and if so, what is it?