Ok, so I don’t know if this is the best way, but it’s working for now.
Within my OOP class (I have a custom plugin to override a WC plugin):
remove_action( 'wp_ajax_wc_function', array( WC_Parent_Class, 'wc_do_stuff' ) );
remove_action( 'wp_ajax_nopriv_wc_function', array( WC_Parent_Class, 'wc_do_stuff' ) );
add_action( 'wp_ajax_wc_function', array( __CLASS__, 'my_override_do_stuff' ) );
add_action( 'wp_ajax_nopriv_wc_function', array( __CLASS__, 'my_override_do_stuff' )
Hope this helps someone and I’d welcome/appreciate if anyone has a better method. 🙂