"The battery is being so heavily modified it isn't the same battery any longer:"
What has not changed, as far as I know, is the cell chemistry. They're still Cobalt Oxide Batteries (COO2). The most volatile and also the most energy dense of all Lithium based battery chemistry's. No amount of shielding will change the chemical properties of that battery. In that sense, the battery remains identical.
What Boeing is doing in my uneducated view, is hazard mitigation, not cause elimination. Maybe charging and discharging them within a narrower band will make the battery more reliable. Maybe not. Until many have been operated for a statistically useful period, nobody will really know for sure. Even if the new shielding makes them safe, that does not speak to reliability.
Why they didn't switch to a different battery chemistry is really beyond me. What Boeing is doing seems too high risk to me.