I can't select an option that is out of stock, it is disabled.

The functionality of which options are displayed and click-able is controlled by BigCommerce and your theme.

The settings for this can be found in your store admin on the Advanced Settings -> Inventory page:

Set when an option is out of stock to > Don't do anything, out of stock options will become selectable again.

We can not override these settings via a script. To modify any current functionality of the option properties, you would have to customize your theme.