Internal hooks for FA actions?

I have seen how there are hooks provided for a custom  module to do its thing but what about hooks in the internal FA code to trigger a custom action when FA does something like create a new invoice?

I am looking at integrating FA with Virtuemart ecommerce which has this sort of hook I describe by enabling user defined class overrides like this:

if (defined('VM_ALLOW_EXTENDED_CLASSES') && defined('VM_THEMEPATH') && VM_ALLOW_EXTENDED_CLASSES && file_exists(VM_THEMEPATH.'user_class/shop_browse_queries.php')) {
    // Load the theme-user_class shop_browse_queries.php
    require_once( VM_THEMEPATH.'user_class/shop_browse_queries.php' );
} else {
    require_once( PAGEPATH. "shop_browse_queries.php" );
}

The VM custom class can then call the parent class. Picture a customisation where VM added a sales order  in FA whenever an order was made through the checkout and when the order was shipped in FA, the VM order status was also updated to show as Shipped.

This would make it very simple to build powerful integration with any system.

Please advise if there is a class override feature in FA.

Rod