Magento 1. Add custom Textfield with dynamic content in system.xml

If you want to add a custom textfield with dynamic content instead of static content from config.xml you can simply add your own data form element like this

place following class under
app\code\local\Varien\Data\Form\Element\YourCustomTextElement.php

	<?php
	/**
	* Magento
	*
	* NOTICE OF LICENSE
	*
	* This source file is subject to the Open Software License (OSL 3.0)
	* that is bundled with this package in the file LICENSE.txt.
	* It is also available through the world-wide-web at this URL:
	* http://opensource.org/licenses/osl-3.0.php
	* If you did not receive a copy of the license and are unable to
	* obtain it through the world-wide-web, please send an email
	* to license@magento.com so we can send you a copy immediately.
	*
	* DISCLAIMER
	*
	* Do not edit or add to this file if you wish to upgrade Magento to newer
	* versions in the future. If you wish to customize Magento for your
	* needs please refer to http://www.magento.com for more information.
	*
	* @category Varien
	* @package Varien_Data
	* @copyright Copyright (c) 2006-2015 X.commerce, Inc. (http://www.magento.com)
	* @license http://opensource.org/licenses/osl-3.0.php Open Software License (OSL 3.0)
	*/
	/**
	* Form text element
	*
	* @category Varien
	* @package Varien_Data
	* @author Magento Core Team <core@magentocommerce.com>
	*/
	class Varien_Data_Form_Element_YourCustomFormElement extends Varien_Data_Form_Element_Text
	{
	public function __construct($attributes=array())
	{
	parent::__construct($attributes);
	$this->setType('text');
	$this->setExtType('textfield');
	}
	public function getHtml()
	{
	$this->addClass('input-text');
	$value = $this->getEscapedValue();
	if (empty($value))
	{
	$value="your custom dynamic content";
	$this->setData('value', $value);
	$html = parent::getHtml();
	}
	return $html;
	}
	public function getHtmlAttributes()
	{
	return array('type', 'title', 'class', 'style', 'onclick', 'onchange', 'onkeyup', 'disabled', 'readonly', 'maxlength', 'tabindex');
	}
	}

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At next you can use your custom form element in system.xml of your module like this. Place your new configvariable in your target field group

	<applicationid translate="label">
	<label>Unique Id of the application</label>
	<frontend_type>yourCustomFormElement</frontend_type>
	<sort_order>5</sort_order>
	<show_in_default>1</show_in_default>
	<show_in_website>1</show_in_website>
	<show_in_store>1</show_in_store>
	<comment>default value is the default encryptionkey from /app/etc/local.xml</comment>
	</applicationid>

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