AMZ QP discounts on existing pre-orders?

[ImPulSive]

If you have a movie pre-ordered and it shows up in your quick picks,

a) do I have to cancel my original order and order it again to get the discount? Or will it be automatically applied to my existing order?

b) does it have to be the exact same format as the pre-ordered item or can DVDs and BDs be considered the same? For example, if pre-ordered the BD version and I get a QP for the DVD version of the same movie, would I get a QP discount on my BD order?

Thanks.