add_filter('woocommerce_order_button_html', 'custom_order_button_text' );
function custom_order_button_text( $button_shop ) {
    $default = __( 'Place order', 'woocommerce' ); // If needed
    $chosen_payment_method = WC()->session->get('chosen_payment_method');

    if( $chosen_payment_method == 'alg_custom_gateway_1'){

    $button_shop = '<button type="submit">Ваша кнопка с нужными значениями и классами</button>';
    }
	
    // jQuery code: Make dynamic text button "on change" event ?>
    <script type="text/javascript">
    (function($){
        $('form.checkout').on( 'change', 'input[name^="payment_method"]', function() {
            var t = { updateTimer: !1,  dirtyInput: !1,
                reset_update_checkout_timer: function() {
                    clearTimeout(t.updateTimer)
                },  trigger_update_checkout: function() {
                    t.reset_update_checkout_timer(), t.dirtyInput = !1,
                    $(document.body).trigger("update_checkout")
                }
            };
            t.trigger_update_checkout();
        });
    })(jQuery);
    </script><?php

    return $button_shop;
}