The system plug-in paths are loaded from two locations:
Plug-ins should add a plug-in path to the plugin.ini file that now exists in the 3ds Max install root. This way, the plug-in is available to all users on the system. An installer should, by definition, have permission to write to the 3ds Max install root. The 3ds Max installer is now responsible for creating a blank template plugin.ini file in the system root.
The User Profile plugin.ini file is used by the user to augment the 3ds Max plug-in paths on a per-user basis. These user paths are exposed to the user in the UI when opening the Configure System Paths dialog and clicking on the 3rd Party Plugins tab. This UI feature shows only those paths mentioned in the user's own plugin.ini file, if it exists, preventing access to system-wide plug-ins in this manner.
There is no definitive method for programmatically locating an individual plugin.ini file in the User Profile directories.
