Tesla can already change its cars' performance with OTA updates. You know what that means, right? It means that all software can be changed with a single OTA update. And much of this system's security depends on how secure Tesla's servers are.

How cars were designed 30 years ago is completely irrelevant, because that's not how all or most new self-driving cars will be designed. They will be designed so that the software can be changed on the go.