Not quite...
The game is /was designed with the "big picture" in mind, meaning that your main interaction with your units should be through your Corps Commanders (in the smaller scenarios they can be Division commanders, really)
But...
You can detach and/or give fairly specific orders to each single unit (which in the larger OOB represent a brigade, in the smaller ones a regiment). It is also possible to give orders to a Division (ie, a group of 2 or more brigades), by clicking on the commander's name that appears when you click an individual unit. Nevertheless this last function is not working well.
Other related things that are not yet implemented are the sublevels of AI between the "grand tactical" and the "Regimental", a reactive "grand tactical AI" (ie, the Ai sticks to an initial plan and allways leaves a Corps guarding her LOP, for instance) and the possibility to take command of a single corps or division in an army commanded by the AI.
Regards