I need someone that really knows Yahtzee well.

I've nearly completed my Yahtzee clone. What I have left is to keep track of Extra Yahtzee Bonuses. These are Yahtzees rolled after an initial Yahtzee has already been scored in the Yahtzee category. I have some questions about this.

1] Must the player use the Yahtzee in order to get the points? In other words, if the player rolls five of a kind on the first roll and then re-rolls a subset of the dice to kill the Yahtzee and uses this new result, does the bonus still apply?

2] If the Yahtzee bonus counts instantly, can the person re-roll a subset of the dice with the same result to score subsequent Yahtzee bonuses on the same turn?