The implication from "hex" is that the hex code of the file was looked at and edited. That can be done with a program named ZTREEv2.2, doubtless there are others. Out of curiosity I tried opening an img file in view mode and found that it will only read the first 892 MB, that is a program limitation as I tried it on a PC with more memory. Regardless I was able to V (view) that much of the file, F9 for search, H for Hex view (slit window between Ascii and HEX and then E for Edit mode. Tab toggles between the ASCII and HEX splits.
I changed North to USA and wrote it back. It worked but I would be sure to try it on a copy to make sure the partial read/write (limited to the first 892 MB) did noting to damage the integrity of the file for it's intended use.