Pre-order button when out of stock? (Prestige 5.x)

Hi all,

I’m looking for a way to apply an ’ if ’ rule for my add-to-cart button, to have to changed to ‘pre-order’ if the variant stock is < 0. Though I’m not sure where in the main-product.liquid code I can do that?

I’ve managed to add a conditional line property for my pre-order products at the moment (if - the template suffix is pre-order’), but I would like to further automate that process.

Thanks in advance!