Magento: Add custom category in navigation

Instead of display the Root category in menu, we need custom category in menu structure:

Copy the Mage/catalog/Model/Observer.php to local Mage/catalog/Model/Observer.php

Current Code:

public function addCatalogToTopmenuItems(Varien_Event_Observer $observer)
{ 

$block = $observer->getEvent()->getBlock();
$block->addCacheTag(Mage_Catalog_Model_Category::CACHE_TAG);
$this->_addCategoriesToMenu(
Mage::helper('catalog/category')->getStoreCategories(), $observer->getMenu(), $block, true
);
}

public function addCatalogToTopmenuItems(Varien_Event_Observer $observer)

{

$block = $observer->getEvent()->getBlock();

$block->addCacheTag(Mage_Catalog_Model_Category::CACHE_TAG);

$this->_addCategoriesToMenu(

Mage::helper('catalog/category')->getStoreCategories(), $observer->getMenu(), $block, true

);

}

Replace Code:

public function addCatalogToTopmenuItems(Varien_Event_Observer $observer)
{ 
$id=$this->getStoreCategories();//call the function of current file

$block = $observer->getEvent()->getBlock();
$block->addCacheTag(Mage_Catalog_Model_Category::CACHE_TAG);
$this->_addCategoriesToMenu(
$id, $observer->getMenu(), $block, true
);
}

public function getStoreCategories($sorted=false, $asCollection=false, $toLoad=true)
{
$parent = '45';//Define the custom Category Id;

$cacheKey = sprintf('%d-%d-%d-%d', $parent, $sorted, $asCollection, $toLoad);
if (isset($this->_storeCategories[$cacheKey])) {
return $this->_storeCategories[$cacheKey];
}

/**
* Check if parent node of the store still exists
*/
$category = Mage::getModel('catalog/category');
/* @var $category Mage_Catalog_Model_Category */
if (!$category->checkId($parent)) {
if ($asCollection) {
return new Varien_Data_Collection();
}
return array();
}

$recursionLevel = max(0, (int) Mage::app()->getStore()->getConfig('catalog/navigation/max_depth'));
$storeCategories = $category->getCategories($parent, $recursionLevel, $sorted, $asCollection, $toLoad);

$this->_storeCategories[$cacheKey] = $storeCategories;
return $storeCategories;
}