Hello,
Once the planned order is converted to production order then that components of BOM in production order are not relevant to MRP. So even if component quantity is changed in production order then on MRP run for this sales order the purchase requisition of component should not change. But the system is changing it what could be the reason for this.
Change Bom in Production Order, then do MRP ,do... | SCN
In above thread too it is stated that changes made in CO02 are not relevant to MRP.
Regards,
Sandip Shrivas