Can I add a 'Pre-Order' button for pre-selling products?

Currently, the app only allows a single button text, which you can edit on the app preference page:

So, this text will display on all products available for purchase in your store, including in-stock products and products available for pre-sell (sold even out of stock).

However, there's a workaround for this. If you need to apply a 'Pre-Order' button for pre-selling items, you may follow the steps described in this article to get this done.