Unlocked ATT S4 on T-Mobile, is T-Mobile upgrade possible?

[BB-Steve]

I'm using an unlocked Galaxy S4 that was originally on AT&T, and is now on T-Mobile. When I tried to upgrade, I kept getting the message that the upgrade was interrupted. I assume it was because it can't talk to the AT&T servers. I manually installed the KitKat upgrade using this process. Any idea if it's possible to do the same thing, but using the T-Mobile ROM without rooting the phone? I'd like to get rid of the AT&T Bloatware.

BTW, I guess this should have been posted in the Rooting, ROMs and Hacks section. Sorry. I'd move it, or delete and repost, but I don't have those rights.