It takes little skill, 15USD soldering iron to solder 4-5 through holes wires, connect 10 usd programmer and flash a new firmware. Investing in a (de)soldering station, with the risk of pulling all the neighboring components, breadboard/something to plugin your new controller or memory into for programming and what not? I’m not sure if I’d go through that trouble

The firmware that's missing on that new chip

That's why you force a full erase to clear the non programmable bit?