Hi guys,
How can I (if at all) disconnect Sales Orders from MRP run so MRP will use only Production Orders?
Thanks.

Create a non-nettable warehouse and use sales orders in this warehouse. MRP/MPS runs only on nettable WHs.
You can transfer materials to this new WH when you just deliver goods to customer.

Just curious: why would you? Any business reason for this?

It this way I don't need to activate MPS module and maintain all items and orders there. Production Orders and MRP Sales forecasts will drive the MRP but not Sales. Some times it helps to disconnect Sales department from the Operations.