E911 setup for different caller ID based on calling location not dialing trunk

We are a school district and have had our Shoretel for 10ish years. We tied our 911 to POTS lines at each school to present the correct caller ID. Is there away to base the caller ID when someone dials 911 to be based on that location or user?

ATT is trying to do away with our POTS lines and move us to a VOIP option instead to replace the POTS lines. Our system was originally on a PRI and about 4 years ago moved over to a VOIP option that the system still thinks is a PRI and ported all our copper lines to it with the exception of one landlines at each school for 911. I can have 911 dial out using a channel instead of the landlines connected to the phone switch.

What is the best way to change the caller ID?