This is not entirely true. The JSON files are just input files, and yes, cannot alter or corrupt the firmware. However, something in those files could cause the firmware to crash or in some way stop working. And it's possible that it could cause this to happen every time the unit starts, making a factory reset impossible. (I'm an embedded software engineer with over 30 years of experience and have seen this happen in systems).
Since the JSON editing trick has been around for several months now and used by a lot of people, it's unlikely that the unit will stop working (what we call in the industry, a "bricked" unit). But it's not impossible.
With all of the above said, I've used the JSON trick several times with very little concern that the POD GO will be damaged/bricked.
