Can you tell yourself in a serious mental tone of voice "My horoscope said I have to pick X" and have it go away?

I haven't tested this, but I'm guessing yes.

Can you do the full analysis and have confident answer without getting it to go away?

Yes. That's when I usually switch to non-content-focused methods.

My quick mental simulations say "yes" to both and that it's not so much 'having an explanation' as it is deliberately flipping the mental "dismiss alarm" button, which you do only when "you" are comfortable enough to.

That does sound pretty plausible.