Default Can't find Carrier specific file download

When I first got my N5, it automatically connects to AT&T LTE network, even when the LTE network has bad connection. Then someone posted a carrier specific file, that allowed my N5 to drop to 3G whenever LTE connection is bad.

I just upgraded to 4.4.3, and need to find that file again. The issue is that I forgot what keywords to search for. Can anyone help?

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