Since self-modification in an unpredictable way is an action that strictly jeapardizes the AGI's future potential to maximize its current utility function (the only basis for the decision concerning any action, including whether the AGI will self-modify or not), the safeguard against unpredictable self-modification would be inherently engrained in the AGI's desire to only ever maximize its current utility function.

I understand the point you are making about value stability.

With our current understanding, an AI with this architecture would not do anything productive. The concern isn't that an AI with this architecture would do something bad, it's that (in light of the fact that it would not do anything productive) you wouldn't build it. Instead you would build something different; quite possibly something you understand less well and whose good behavior is more of an empirical regularity (and potentially more unstable). Humans as the output of evolution are the prototypical example of this, though many human artifacts have the same character to varying degrees (programs, organizations, cities, economies).