Can demand change of Assembly lead to a new gross demand of related component by item supply plan?

Hi, Anyone has experience to be able to calculate the new demand quantity of component when there is a demand change of the related Assembly item, not considering the component's inventory and quantity on PO/TO? The scenario is that :

1) the first demand forecast for Assembly A is 100 quantity, then after running the supply plan, carry out a purchase order for component item B for 100 quantity (assuming 1:1) with pending approval status.

2) in the second planning cycle, the new forecast quantity for Assembly A is 80; the customer want to be able to get the result of new demand quantity of the component item B is 80 , even though there is already a purchase order for this component item for 100 quantity.. But in standard Item supply plan, system will not suggest new demand of component for 80 because the existing PO quantity is larger than the demand.