We are talking about Tzeentch - The changeling. This guy got a nasty ability: Arch-deceiver: At the start of the battle, you can set up the Changeling in your opponent’s territory as though it were part of their army. Enemy units treat it as part of their own army – they can move within 3" of it but they cannot target it with spells or attacks, and so on. If it attacks, casts or unbinds a spell, or is within 3" of an enemy Hero in your opponent’s hero phase, it is revealed and this ability no longer has an effect. Now, the question. While he's "disguised", can he control objectives for the Tzeentch army? Reasons for NO: to contest an objective is an active action in favor of your army, you cannot do it without revealing it. To have a model that can control obectives almost without risk is just wrong. Reasons for YES: to take an objective is not listed in the actions that reveal the Changeling, and to control an objective you need to have a model nearby it. The Changeling in "disguise mode" is just a model that the opponent doesn't care about. I would like not only your opinion on the matter, but most of all, if you have some piece of rule or some evidence to support one answer over the other (be it the opinion of a GW referee, or whatever)
I think he would be able tot controle an objectieve. He stays part of the tzeenth army, the only thing is that the enemy doesn't know it is part of the tzeenth.
Maybe I haven't even fully understood how it works. You really set up the model? So your opponent knows it is there but they have to move a hero near it and pray for the double turn otherwise they cannot kill it and cannot prevent it from claiming/contesting an objective? Just a quick note: It would be way cooler if your opponent didn't even know, and you could use one of HIS models (writing down a note describing it, like "the Ardboyz unit's banner bearer" at the start of the game) until you reveal it. Hmmm..... Anyway let's get back to the rules: I looked through some battleplans and most of them ("Take and Hold" and "Gifts from the Heavens" being contrary examples) just say you have to have more models near an objective than your opponent, so I'd say yes, the Changeling can contest them but he will only be able to claim them if he is alone. I don't see why he shouldn't be able to. So that basically means if you are playing against a Tzeentch opponent with the Changeling in his list you have to make sure that if there is a objective in your territory you have to place a unit there that can likely survive one turn of battle with the Changeling, preferably a hero that is not a wizard. That way you can prevent the Changeling from getting a free objective claim in your territory claim if your opponent has the first round. The "Three places of Power" battleplan makes that very important.
Yeah, that's probably the most sensible way to play it (waiting for some official statement on the matter).