Customising Indivual Objects

As Pete indicated, iApps and iRules are two different BIG-IP "tools" with two completely different purposes. iApps are used to deploy and manage common application configurations, such as Exchange. You can change the application's configuration data using the iApp's Reconfigure function or manually (using Configuration utility or tmsh) if you turn Strict Updates off. (The latter is not generally recommended.) Without an iApp, you must manually create and maintain configuration using either the Configuration utility (GUI), tmsh, or the iControl API from an external program.)

iRules themselves don't do anything with respect to updating configuration data. iRules are used to control traffic behavior during traffic processing.