Yes it is possible with lots of searching and hacking. It is way easier to do permanent SIM unlock procedure and easier than that, use a custom ROM. See link:
Here's my knowledge from the conversion. I could follow the steps in that post but the phone never really worked right. The steps to make the phone work on GSM carriers caused menus to disappear from within the phone, such as ability to change APNs. It works but there's a better way.
I flashed an AOSP ROM to my phone. Shameless plug here for LiquidSmooth beta, I've had the least problems getting a working phone with that ROM, actually works out of the box. While on AOSP, I can replace my Sprint LTE SIM with that of another carrier, reboot the phone and then go to the *#*#4636#*#* menu and change radio mode to GSM. I'm using an AT&T SIM now, domestic even and can SMS, MMS and have HSPA+ data, no LTE. If for some silly reason I want to switch back to Sprint, just swap SIM card, reboot phone, change radio mode in the hidden menu. Simple.