The directory where these are stored appears to have changed in recent software releases. On my system, I had several folders that had location files. The folder that is actually active in my Pogoplug is
/usr/local/share/tvheadend/data/dvb-scan/atsc
Here is how I figured it out by brute force.
1. I searched the entire drive for a known location name like, us-ID-Boise.
2. I when to every folder that contained this location file and renamed each to something unique.
3. I restarted TVH and then looked to see what unique name appeared for us-ID-Boise. This told me what folder to place my edited location file in.
I am sure there is an easier way, but this worked for me.
--- Steve