You can block backorders on an item but still allow the /VA option (allows sourcing from another CODIS distributor). From the main CODIS menu, go to 20/30/70, Product File Editor. Enter the manufacturer and item number you want to edit. Change lines 10, 11, and 12 to “No”.
Change line 62 to “Yes”.
Update the record.
The item will now NOT allow backorders but still allow sourcing an out-of-stock item from an alternate CODIS vendor. You can set these flags at the product code level as well (70/110 from the main CODIS menu).