[Responding to an old comment, I know, but I've only just found this discussion.]

Never mind special access protocols, you could make code unmodifiable (in a direct sense) by putting it in ROM. Of course, it could still be modified indirectly, by the AI persuading a human to change the ROM. Even setting aside that possibility, there's a more fundamental problem. You cannot guarantee that the code will have the expected effect when executed in the unpredictable context of an AGI. You cannot even guarantee that the code in question will be executed. Making the code unmodifiable won't achieve the desired effect if the AI bypasses it.

In any case, I think the whole discussion of an AI modifying its own code is rendered moot by the fuzziness of the distinction between code and data. Does the human brain have any code? Or are the contents just data? I think that question is too fuzzy to have a correct answer. An AGI's behaviour is likely to be greatly influenced by structures that develop over time, whether we call these code or data. And old structures need not necessarily be used.

AGIs are likely to be unpredictable in ways that are very difficult to control. Holden Karnofsky's attempted solution seems naive to me. There's no guarantee that programming an AGI his way will prevent agent-like behaviour. Human beings don't need an explicit utility function to be agents, and neither does an AGI. That said, if AGI designers do their best to avoid agent-like behaviour, it may reduce the risks.