A previous ruling on Fancy New Hat will be reversed. In the interest of clear understanding of the language used, Fancy New Hat only protects the bearer from influence reductions of opponents cards while he is wearing the hat.
If he was already hit by a Blood Curse earlier in the turn, giving him a Fancy New Hat will not remove that penalty.
It will prevent another Blood Curse from being used on the dude wearing the hat, because his influence can not be reduced by other players card abilities.
In short, it only protects the dude from abilities that target him while he has the hat. Previous modifiers remain in play until their original ‘end’ occurs.