We can open the Purchase Order to manually change the Vendor Name to another vendor, however, users may want to show a specific vendor other than the Preferred Vendor even prior to the creation of the new PO.
To do this, we follow the steps below:
1. Navigate to Setup > Customization > Transaction Forms > Click Edit next to the Sales Order set as preferred form.
2. Click Screen Fields tab > Columns sub-tab > Check the box Show for fields PO Rate & PO Vendor.
3. Hit Save
4. Navigate to Transactions > Sales > Click Enter Sales Orders
5. Set the Customer Name and all other fields
6. Under the Items tab > Select either a Drop Ship or Special Order Item
7. Notice the field PO Vendor defaults to the Preferred Vendor set in the Item Record > Click the drop down to see list of Multiple Vendors > Select the Vendor for the Purchase Order.
8. Hit Save
9. In the Processed Orders page, click Processed Number link to view the related Purchase Order. The Vendor Name shows the vendor selected in Step 7 instead Preferred Vendor.