The last one proposed it's not really modular. Subcontrollers modules cannot be ported easily to other project without "picking" each component from common models/controllers/views/libraries/etc directories. Anyway I appreciate your suggestion!
It is matter of semantics what is really modular. If your "subcontrollers" folder is named "admin", then OK, avoid the third way. The routes.php rules might be a better choice, I have seen it within PyroCMS.
For "admin" there is the fourth way - a separate application, but that is a long story.
CI only loads it from application/config, you can set different configs in the database.php and then
switch them later. See the database configuration in the Users Guide.
Yeah I know that but I wanted know if there's no way to load it from module/config with HMVC.
Because as you say, if I set different configs in the database.php I should switch them later with different value for $active_group.
You seem tell me that it's impossible, so I will change the $active_group value in my constructor method of my controller.