A few examples (in approximately increasing order of controversy):
If you proceed anyway...
- Identify knowledge that may be dangerous. Forewarned is forearmed.
- Try to cut dangerous knowledge out of your decision network. Don’t let it influence other beliefs or your actions without your conscious awareness. You can’t succeed completely at this, but it might help.
- Deliberately lower dangerous priors, by acknowledging the possibility that your brain is contaminating your reasoning and then overcompensating, because you know that you’re still too overconfident.
- Spend a disproportionate amount of time seeking contradictory evidence. If believing something could have a great cost to your values, make a commensurately great effort to be right.
- Just don’t do it. It’s not worth it. And if I found out, I’d have to figure out where you live, track you down, and kill you.
I wouldn't claim that any human is actually able to describe their own utility function; they're much too complex and riddled with strange exceptions and pieces of craziness like hyperbolic discounting.
I also think that there's some confusion surrounding the whole idea of utility functions in reality, which I should have been more explicit about. Your utility function is just a description of what you want/value; it is not explicitly about maximizing happiness. For example, I don't want to murder people, even under circumstances where it would make me very happy to do so. For this reason, I would do everything within my power to avoid taking a pill that would change my preferences such that I would then generally want to murder people; this is the murder pill I mentioned.
As for swapping the utilities of spinach and cheesecake, I think the only way that makes sense to do so would be to change how you perceive their respective tastes, which isn't a change to your utility function at all. You still want to eat food that tastes good; changing that would have much broader and less predictable consequences.
Only if your current utility function is "maximize expected utility." (It isn't.)