... from
Warhammer Community:
A lot of stuff (too much to copy and paste it all here). Here's the highlights:
Q: When a rule allows a model or unit to take an action (move, shoot, charge, fight or attempt to manifest a psychic power) outside of the normal turn sequence, and that rule explicitly mentions to make that action as if it were a different phase of the turn structure to the current one, e.g. ‘That unit can shoot as if it were the Shooting phase’, do rules that are normally used during that phase (in the example this would be the Shooting phase) take effect? Is the same true of Overwatch attacks?
A: With the exception of Stratagems, all rules (e.g. abilities, Warlord Traits, psychic powers etc.) that would apply in a specific phase apply to actions that are taking place ‘as if it were that phase’. However, if a Stratagem specifies that it must be used in a specific phase, then it can only be used in that phase (e.g. you cannot use a Stratagem that says ‘Use this Stratagem in the Shooting phase’ to affect a unit that is Shooting ‘as if it were the Shooting phase’). For the purposes of this FAQ, Overwatch attacks are not considered to be attacks made as if it were your Shooting phase.
Q: Can the Opportunistic Advance Stratagem be used when a unit is affected by the Swarmlord’s Hive Commander ability, the Overrun Stratagem, or the Mind Eater Warlord Trait?
A: Yes in all cases. Please note the FAQ above regarding moving multiple times in a single phase.
Q: If a unit is affected by a rule that forces it to fight after all other units able to fight have done so, such as the effects of the Paroxysm psychic power, the Vexator Mask or the Armour of Russ, can it still be affected by the Counter-offensive Stratagem?
A: Yes, the Counter-offensive Stratagem allows a unit to fight outside of the normal fight order (i.e. the Stratagem does not give a unit the ability to fight first in the Fight phase, it simply instructs you to pick a unit and fight with it next).
Q: Can the Counter-offensive Stratagem be used to negate a unit fighting last because of the Vexator Mask Artefact?
A: Yes, the Counter-offensive Stratagem allows a unit to fight outside of the normal fight order (i.e. the Stratagem does not give a unit the ability to fight first in the Fight phase, it simply instructs you to pick a unit and fight with it next).
Q: If a unit is under the effects of the Paroxysm psychic power, can the Counter-offensive Stratagem be used on it?
A: No, because it is not ‘eligible’ to fight until every other unit has done so.
There's also changes to the T'au Empire, Deathwatch and Space Wolves
FAQs.
At least they gave this one for free instead of forcing you to buy Chapter Approved.