Write a custom code to always allow backorders (Woocommerce)

I am looking for a solution to fix the way the Lightspeed POS works with Woocommerce. Lightspeed syncs the stock and automatically sets the stock status on 'Out of stock' when stock level is zero. This will disable customers to place backorders even though this should be possible.

Use case: When stock reaches 0 always set stock status on 'In stock' instead of 'Out of stock'. This should enable customers to add products to cart even though there is no physical stock.

The add to cart button should always be enabled. When stock is zero there should be a notification that says '2 dagen levertijd' (shipping within 2 days).
When available stock the text should say 'x op voorraad' (x in stock). Out of the box Woocommerce logic. Stock display format.