Both players and Non-Players are part of a chain of command. Though superiors are not supposed to interfere in decisions made by their juniors they can do so.
The following influence are recorded in the rules: Asking a commander to volunteer (command or part of) for the front (or substitute), Seek or Block appointments, embezzlement trials, admittance to a regiment, excuse from duties, title rolls, and investments. Take the first one, a commander can either volunteer their entire unit or a portion of their command (and need not accompany it). In this case a colonel can, by volunteering, essentially order a squadron/battalion to the front. This could be extended therefor to the brigadier instead of volunteering the reqigment, get the commander to just volunteer a battalion.
Nominally the regiments are independent organizations, with the Colonel historically "owning" the regiment, however if a subaltern is trying to be excused from extra duty, while at the same time trying to see the mistress of the regimental commander, the commander would likely order the Major to not excuse this subaltern.
This type of exchange becomes more important in games where holders of posiitions can be sacked, and other house rules allow variations to the operation of a regiment. e.g. see Regimental Finances
Allow players to influence higher officers to make officers under them perform actions that are otherwise influencable. This could be used to make opposition more difficult. Similarly if a player holds such a senior position then then can freely influence junior officers.
Orders across the regimental boundary (e.g. General Staff down to Regimental personnel) should be considered differently. Also constant meddling by senior officers may not be appreciated.