I really need the possibility to add another bum of entries to the menu. I would love to make a new button and have some sub entries then.
First question: Is there a simple way to do it?
Second question: Wouldn't it be great to do such things in 1.0.1 in the admin center (such as custom profile fields -> custom menue entries)?
You can use a hook to do anything you want with the admin menu. You create your own function that will take $admin_areas array. This array is in the Admin.controller.php I think. You modify that array to insert your menu items into it. I think Spuds created a nice function to modify menu items too.
You register your function by inserting an entry into the database giving the name of the hook, with the name of your function, and the path to the name of your file for the custom function. I'm not sure which table it is at the moment because I haven't been keeping a close eye on the code here for a while. After a quick look on Github, take a look at the creatMenu() function in the Menu.subs.php file. It takes a $menuOptions array that will then use the call_integration_hook() function to call your custom method.
Sorry I don't have in depth details for you. But that can get you started. :)