Task organizing IS a thing in HoI4 (this is a change from the title of this thread).
Given how many divisions there are in a typical game as Germany or the Soviets, I like to think that my Task Organizing Units are, in fact, the shells generals command which contain divisions.
Sure. That makes sense.
Players can task organize Armies and Army Groups.
As the comments point out, the game sort-of, but sort-of-doesn't portray the upper echelon independent assets pushed to subordinate units for special missions.
The glider, supply, and fortress-busting artillery special abilities of field marshals give the flavor of Army-Group-level commands helping out lower level commands.
Nice feature.
As Secret Master and Fulmen point out,
To add to Fulmen's thoughts on the subject, the only way I'd think it would work to implement corps and army level assets would be to have something akin to "support companies" except at the Field Marshal or General level.
You could have slots for your 24 division groups and for your 5 army groups. You could tell the game to add, say, a battalion of TDs or whatever to one of these special slots. These TDs would provide some kind of either command ability or army wide buff to all those divisions.
I don't know if it would be very fun, and I'm sure that AI would screw it up. But it would let you simulate higher level assets.
If this was an essay for publication, this would be a good place to give 3 historical examples.
Corps level artillery supporting a divison's breakthrough.
Army level transportation units moving a corps
Station hospitals caring for an Army Group.
But, instead, we'll let the division level assets identified in the OP stand-in for all possible examples.
These RAJ and UK division level units supported the subordinate brigade-sized units in their 1935 operation.
This pattern is repeated at each echelon (for most nations, that is...the post-purge USSR had a different organizational structure that diminished command-and-control*)
- Brigade commanders push out (detach) brigade assets to help battalions/regiments
- Division commanders push out (detach) division assets to help brigades
- Corps commanders push out (detach) corps assets to help divisions
- Army commanders push out (detach) army assets to help corps
- Army Group commanders push out (detach) army group assets to help armies.
And so it goes.
*USSR did away with its corps after the purge. For some reason, the Soviet Union did not have enough officers to staff all the headquarters. By removing an entire echelon from its formation, the USSR was able to spread out its remaining officers more thinly over the Soviet Army. This resulted in Army commanders exceeding their span of control.
(nice game design feature...in HoI4, commanders' abilities diminish when they command too many subordinate units. A span of control is typically 3 to 5 line units.)