MRP and Open PO

Hi all,

Our client till now have not used MRP. But now they are planning to use it. Every settings for MRP is done. But their requirement is "for a particular PO(which was created before MRP), 1000 quantities of a material are pending for GR. Out of 1000, only 750 should be considered for MRP". So my question is

1. Is it possible to do like this?

2. If yes, what can i do for rest 250 quatities? for the time being should i do some issue or something??

Please help me on this

Thanks.

Rosh