Adding a custom option using an extension in Magento - magento

Question

I'm creating a custom extension and I would like to add a custom option when a certain item is purchased.
For example, when the product "Name Tag" is purchased, the extension would detect that the specific product has been ordered and assign a custom option of "Year" to it. The user does not see this, but the attribute is added and displayed in the admin when viewing the order.
Are there any specific listeners our there to accomplish this?
EDIT Based on Ben's suggestions in the comments, I'm editing the comment to reflect progress I've made with the answers located here: https://stackoverflow.com/a/9496266/268165
I now have an extension running under Namespace_addYear and the following code running:
Namespace/addYear/etc/config.xml:
<?xml version="1.0" encoding="utf-8"?>
<config>
<modules>
<Namespace_addYear>
<version>1.0.0</version>
</Namespace_addYear>
</modules>
<global>
</global>
<frontend>
<events>
<catalog_product_load_after>
<observers>
<Namespace_addYear>
<type>model</type>
<class>addYear/observer</class>
<method>catalogProductLoadAfter</method>
</Namespace_addYear>
</observers>
</catalog_product_load_after>
</events>
</frontend>
</config>
Namespace/addYear/Model/Observer.php:
class Namespace_addYear_Model_Observer
public function catalogProductLoadAfter(Varien_Event_Observer $observer)
{
// set the additional options on the product
$action = Mage::app()->getFrontController()->getAction();
if ($action->getFullActionName() == 'checkout_cart_add')
{
// assuming you are posting your custom form values in an array called extra_options...
if ($options = $action->getRequest()->getParam('extra_options'))
{
$product = $observer->getProduct();
// add to the additional options array
$additionalOptions = array();
if ($additionalOption = $product->getCustomOption('additional_options'))
{
$additionalOptions = (array) unserialize($additionalOption->getValue());
}
foreach ($options as $key => $value)
{
$additionalOptions[] = array(
'label' => $key,
'value' => $value,
);
}
// add the additional options array with the option code additional_options
$observer->getProduct()
->addCustomOption('additional_options', serialize($additionalOptions));
}
}
}
}
The Observer.php was taken from the answer linked above. So far, I cannot get the store to do anything other than display a 404 page when I remove the tags in config.xml.
Is there anything someone can immediately see that is wrong?