Project Planning in Parts Or Time based

Hi

We created a project through CJ20N and Assign FG Material Qty = 100 MT. Then we run MRP through MD51. Client do not want to create PR of raw material Required for production 100 MT at once. He wants to plan FG in parts. Means Sep 2016 = 40 MT, Nov 2016 =60MT. Please suggest how we can handle this situation.

As per our business we have 30 -40 Material for one project & if we edit requirement twice it become 60 fg. we do not want to assign each material twice.

Please suggest how can we plan as per time period.Like 40 MT in Sep & 60 MT in Nov with out entering requirement multiple times.