This is not the case with the file used to control the contact form(app/code/core/Mage/Contacts/controllers/IndexController.php,) as it is a controller and so it needs to be overloaded in a different manner.

Instead, you will need to create a custom package, or plugin, in-order to make your changes update-proof.

Make a Backup

As is the case with any sort of modification, make a backup of your Magento Directory and database before continuing!

Overview for Overriding the Mage_Contacts_IndexController Class

The basic process is thus:

1. Add Your Module, which over-rides the Contact Controller, to your /app/code/local Directory
2. Add an xml file to /app/etc/modules, activating your new custom module
3. Clear Magento Cache(System->Cache Management-> Refresh All and Flush Magento Cache

Adding Your Module to the Local Folder

First, you will need to create the folders/files necessary for your module. You can download this example here: Magento Contact Extended

The KCR folder should be uploaded to the /app/code/local/ directory and has the following structure:

KCR
|-- ContactExtended
    |-- Helper
 	-- Data.php
    |-- controllers
    	-- IndexController.php
    |-- etc
 	-- config.xml

The files are as follows:

/app/code/local/KCR/ContactExtended/etc/config.xml

<?xml version="1.0"?>
<config>
    <modules>
        <KCR_ContactExtended>
            <version>0.0.01</version>
        </KCR_ContactExtended>
    </modules>
    <frontend>

        <routers>
            <contacts>
                <args>
                    <modules>
                        <KCR_ContactExtended before="Mage_Contacts">KCR_ContactExtended</KCR_ContactExtended>
                    </modules>
                </args>
            </contacts>
        </routers>

    </frontend>

    <global>
        <helpers>
            <contactextended>
                <class>KCR_ContactExtended_Helper</class>
            </contactextended>
        </helpers>
    </global>

</config>

/app/code/local/KCR/ContactExtended/Helper/Data.php

<?php
class KCR_ContactExtended_Helper_Data extends Mage_Core_Helper_Abstract
{

}

/app/code/local/KCR/ContactExtended/controllers/IndexController.php

<?php
require_once 'Mage/Contacts/controllers/IndexController.php';
class KCR_ContactExtended_IndexController extends Mage_Contacts_IndexController
{

 public function postAction()
    {
	echo 'GOOD!';
	die;
	//parent::postAction();

    }

}

Note that the above will simply print “GOOD!” and die, breaking your contact form. You would want to modify ‘KCR/ContactExtended/controllers/IndexController.php’ as needed.

Activating Your Module

Now that you have your module added, you need to tell Magento about it. Upload KCR_ContactExtended.xml to your /app/etc/modules/ folder.

It should be as follows:

/app/etc/modules/KCR_ContactExtended.xml

<?xml version="1.0"?>
<config>
    <modules>
        <KCR_ContactExtended>
            <active>true</active>
            <codePool>local</codePool>
        </KCR_ContactExtended>
    </modules>
</config>

Clear Your Cache and Verify Module is Found

Next, clear your cache in Magento, by logging into the admin backend and going to System->Cache Management

Select all and refresh, as well as going ahead and clicking on “Flush Magento Cache”

Next, goto System->Configuration->Advanced. You should see your new module listed under “Disable Modules Output” with the name “KCR_Contact_Extended” and it should be set to “Enable”

Verify it is Working

The file “/app/code/local/KCR/ContactExtended/controllers/IndexController.php” overloads the postAction function. When you submit a contact form, it should now print “Good!” and then php should die.

You would obviously want to change this and can override any of the functions in Mage/Contacts/controllers/IndexController.php in a similar manner. Notice that you can also use “parent::postAction();” if you wanted to still call the default ‘postAction’ function.

Getting Help

Hopefully this will help some folks out and please don’t hesitate to comment and I will try to reply as best I can.

The above process works correctly in Magento 1.6 and 1.7 for me. However, Magento is rather complicated, with the documentation and community support forums often leaving something to be desired. So, before attempting the above, you should have a somewhat established understanding of php.

Please note that my main goal was to change the redirect, add better support for multiple forms, and provide a bit better spam/user tracking. As such, being able to over-ride the postAction function was my main need.