Yes, you can always sent courier messages to units even if they are TC'd.
"when its set to none the orders are executed immediately" this is when you TC the unit and give direct orders right?
Regiments don't have stances, (attack, defend, etc.), only brigades and above have those. If you TC a brigade that had a stance of 'Probe', for example, then un-TC it, it will now have a stance of 'None'. If you do not give it a new stance, the brigade commander will give himself one after a while based on his characteristics. In my experience, it's not usually the one I'd have chosen.
Also note that the AI is very human-like. If a regiment, brigade, etc. is busy doing something, like fighting off the enemy, and you give it an order to move somewhere else, that commander will usually just put the order on his to do list. He deals with the problem at hand first, since he feels that he has a better idea of what's going on in his immediate front.
Secession is futile.