Over the years we have had several customers ask to be able to set a different flushing method than on the item flushing method for a particular components(s) on a production BOM. You can change it on the production order bom but you cannot set a value per the "standard BOM".

I would think in the BOM the field would be blank or user entered vs inheriting from the item when the BOM is created.

If it is left blank when a production order is refreshed it would use the value from the item as it does now. If there was a value entered when the BOM is created, it would use the value on the production bom vs from the item.