Yes, there is a filter for the express checkout button ‘woo_vipps_cart_express_checkout_button’ taking a button and the URL and returning a new, formatted button. You can also change the button with CSS.
To move the button, you will ned to do remove_action on ‘woocommerce_cart_actions’, the action would be array($Vipps,’cart_express_checkout_button’) where $Vipps is the global singleton Vipps object. Or iterate over the actions and remove it like that. Then add this action to a Woo template action of your choice.
Upcoming is a filter ‘woo_vipps_show_express_checkout’ that will allow you to disable the button more easily.
You can also add the button by shortcode [woo_vipps_express_checkout_button].
If you need more actions and filters, just tell us about them and we’ll consider adding them.