Hello
Technically speaking, the sales orders are read from table VBBE, so MRP and demand management will consider the sales order date from this table.
It means that, if the date changes on table VBBE, it will also change for MRP and demand management, which means that the sales order can be allocated to another PIR.
The only solution that I can think for this issue is to use BAdI MD_CHANGE_MRP_DATA, in order to manipulate the sales order date, so that MRP keeps using the original date, even after running V_V2.
Regards
Caetano