Downgrade my Z30 from 10.3.3.xxxx to 10.2.1.xxxx (OEM) possibility?

Hi All - great community!
So when I upgraded SW OTA on my new ST100-5, I still had my OEM (TMO) splash screen and T-Jingle (which I prefer), but then I inadvertently did a restore from my LEAP and lost all the OEM TMO stuff. Any way to totally scrub the phone OS then load the OEM image (which I found on CrackBerry)?

You can't downgrade to anything below 10.3.3 once you're on 10.3.3.