add_filter( 'woocommerce_product_add_to_cart_text' , 'custom_woocommerce_product_add_to_cart_text' );


function custom_woocommerce_product_add_to_cart_text() 
{
    global $product;
    $product_type = $product->product_type;
    switch ( $product_type )
    {
        case 'external':
        return __( 'More', 'woocommerce' );
        break;
        case 'grouped':
        return __( 'More', 'woocommerce' );
        break;
        case 'simple':
        return __( 'More', 'woocommerce' );
        break;
        case 'variable':
        return __( 'More', 'woocommerce' );
        break;
        default:
        return __( 'More', 'woocommerce' ); 
    }
}