but I don't know of any ICE models where the difference is solely software that locks features down (or, as you said, drilling a hole somewhere to limit functionality). They may share parts like bodies or engine blocks (not sure, I'm not a mechanic) - but there's a lot of additional hardware that makes it safe for them to beef things up via software.
not sure though - can you think of any two ICE models where difference between the two is solely locked down via software? or the only difference is a hole drilled in a cylinder, etc etc. It may exist and I'm just not aware of it.
https://www.whatcar.com/bmw/1-series/hatchback/review/on-the...
b) I'm on mobile, cannot find exact models now, but yes, there were two engines having the same engine block&head, acessories, turbo, powertrain and were only tuned differently in ECU. Not sure now if it was for the same model of the car itself, though, maybe it was used across different model series. And a pretty common practice in European diesel cars with average power, loading ECU maps from higher versions - although often, the car would have smaller brakes or less Nm rated powertrain.
Diesel trucks tend to be like this too. If I recall they put the same 7.2L engine in a bunch of F-250 to F-550(although there your also paying for better built frame/suspension) models.
Easier to validate and build one powertrain on the assembly line than 2-3 variants.