AHADMIN is the COM API that IIS 7.0 uses for reading and writing its configuration system. One of the not so well known features is that you can also use the same API to manage Administration.config by calling the SetMetadata method and specifying that you will be targeting Administration.config. What this ends up doing is using an IAppHostPathMapper built-in mapper that will re-map the files so that you can manage Administration.config easily.
Here is an example of a common operation that adds a ModuleProvider (UI Extensibility Module) and its corresponding Module.
I'll use this time to also mention that it is very important to add it to the Modules section in case you want your module to be used from Site and Application delegated connections, otherwise only Server connections will get them.