Can I use hand of fate if I have less blessed tokens than combined enemies attack and horror values?
Hand of fate question
Yes. Cancelling the attack happens whether you add tokens or not because of the "then" indicating that adding tokens only happens after you cancel the attack. You'll perform as much of the action as you can, putting however many bless tokens you have in the bag, because it's an effect of the spell and not a cost.
Hope that helps!