Sorry for the delay. Real life gets in the way now and then. My opinions on these are as follows. I would like to see other peoples opinions as well.
#1: Good question. As there is two Hell Claws, I would say that destroying one of them would result in the loss of one bonus granted by the claws (IE, Penetrating +1 or +1d6 to CAF), probably determined at random. Only when both claws are Destroyed would they be rendered useless.
On the other hand, the above is a bit too logical for Chaos, so perhaps roll on the following chart when one Hell Claws location is destroyed. Yes, I just made up the chart as I am typing. Because Chaos.
D6 _ Result
_ 1 _ No effect. Hell Claws continue working as normal.
2-3 _ Hell Claws lose the Penetrating +1 effect, but otherwise continue working as normal.
4-5 _ Hell Claws lose their +1d6 to CAF effect, but otherwise continue working as normal.
_ 6 _ Hell Claws are destroyed and cease functioning.
#2: That depends on what you mean by 'retroactively'. Note the final sentence of the first paragraph of the second column on page 6 of the Chaos book.
Thus the "Brightly Patterned Skin" Reward card (or any of the others that do the same thing) would have no effect if played after your foe made his attack rolls. To have effect, it would have to be played before the rolls were made, but could be played after targets are declared.
As another example, the "Oozes Slime" Reward card (or any similar) would have to be played before the saving throws were rolled in order to have their effect. If you roll the saves, then play the card, it was wasted with no effect. On the other hand, if played on a detachment of models (that do not normally have saves) after hits are determined, but before casualties are removed, they now gain saves.
The Telekinesis card, could - in my opinion - be used upon a model that has already acted that turn as the effect is not really dependent on the model. Evil Eye on the other hand could not, as it grants the chosen model with an actual attack.
#3: I would agree that the controlled detachment could fire upon their prior allies, due to the phrasing of: "You take it over for this turn and choose where it will move and what it will attack..." To me, that says that - for all intents and purposes - that detachment is part of the Slaanesh army for that turn, and may act accordingly. However, a side effect of that would be that if the opposing side manages to break the target detachment, they get the VP for what was previously their own forces.
#4: I interpret the adding 25cm bit as applying to any forces at 'Grounded' or 'Low Altitude'. It should not apply to other models at 'High Altitude', but with the current wording that is possible. I suppose it could represent such models moving rapidly and the difficulty in targeting them, but that would render the weapons on most Flyers useless against other Flyers at High, as most such have Weapon Ranges of 25cm. At least, I think they do. I have not checked that, so I could be wrong.
#5: I have no idea what was intended, but the description makes more sense if you place the sentence about models with fields / shields before the one about being killed with no save. In other words, the power is applied as follows:
_ Does the target have Fields / Shields? If yes, the owner of the target model rolls D6 and ignores the effect on 4+.
_ Roll D6 for each remaining affected target. On a 4+ it is destroyed (no save allowed), unless it is a Titan or Praetorian. If a Titan or Praetorian, roll on the Head or Bridge damage chart.