That said, it's far from the most easily accessible formulation of that meaning imaginable.

I mean, sure, the future state in which half of my measure has ~1 confidence in "heads" and half my measure has ~0 confidence in "heads" is in some sense not a change from my current state where I have .5 confidence in "heads", but that's not the interpretation most people will adopt of "leave your beliefs unchanged."

It seems more accessible to say that if I expect a test to update my beliefs in a particular direction, I should go ahead and update my beliefs in that direction now (and perform the test as confirmation).

Of course, this advice presumes that I won't anchor on my new belief. Which, given that I'm human, is not a safe assumption.