Well, on the bright side you should be able to turn it off anyways using something along the lines of a widget. Like, an LTE on/off widget. I don't know for sure though, I'm only speculating because I know that a lot of widgets or apps can actually disable and enable features you normally wouldn't be able to change in the settings.
I havent heard of an app/widget that does that as of yet, but that doesnt mean that somebody won't create that. So far the only network switching phones i've heard of have been Non LTE devices (GSM/WCDMA) i've never heard of an LTE device (PHONE) where you can turn off the radio and use only other 2G/3G radios.
And I'm wondering why that is. What if I just want to use 3G? I'm sure an LTE handset using 3G would have great battery life. And when I want to stream data or plan on using data extensively I'll just turn on the LTE radio. It's just a common sense thing, you know?