So there a few cards that say spend a dice to reroll x number or change one accuracy to a hit and so forth. Does the player spend the dice before the roll. Or roll then choice a dice that comes up blank?

P 2 of the Rules Reference.

Modify Dice occurs after Roll Attack dice. Modify Dice includes adding and spending dice due to card effects or concentrate fire.

So, spend those blanks.

You spend the dice before rerolling any other dice.