Okay verdict is in.
:drum roll:
It totally works.
You need a Simcard from any other provider who's towers show up when you SCAN for them and if they are in the provider box in the change provider settings. In my case I use Google Fi and they operate on several providers, for this example I'm using T-mobile's towers.
Once you verify you can see Towers from a provider it means you have that Frequency of radios and can connect to them.
Power off the unit and get on the roof and swap the sim card from Winegard's ATT sim to provider of your choice's sim card.
Once that is done power on the unit. Wait ~90 seconds for it to come online and connect to its wifi signal.
Once connected browse to 10.11.12.1 in your browser (I don't believe you can change provider settings in their app).
Login using admin as the username and the password that you can get from the app's settings, or whatever you may have already reset it to. This is not the same password that the wifi network uses.
Once logged in go to the drop down box at the bottom that says navigate to page, select Change Provider. You'll now use the drop down and pick the provider in question. You now need to change the APN setting to whatever the provider requires. In my case for Google Fi is it h2g2. Save and the unit will restart and connect to the towers using the new sim.
My last step was to use whatismyip.com to verify it was indeed on T-mobile's network.