Can be set to 'yes' or 'no' and determines if this object with CanDisguise=yes set only disguises when it is not moving rather than a permanent disguise.
Note that, contrary to an intuitive reading of the flag's name, this does not actually cause vehicles in question to loose their disguise when changing position - any vehicle with CanDisguise=yes will loose its disguise when moving (unless it also has PermaDisguise=yes, which has problems of its own when used on vehicles). What DisguiseWhenStill actually does to vehicles is cause them to adopt the default Mirage Tank behaviour of assuming a disguise without having to obtain it first by firing on a terrain object with a weapon with MakesDisguise=yes on the warhead. While it is possible for such a vehicle to adopt a different disguise via such a weapon if it is given one, it will, right from the War Factory and upon ceasing movement, by default disguise as one of the terrain objects listed in DefaultMirageDisguises, without having to adopt a disguise first. If a vehicle is given CanDisguise, but DisguiseWhenStill is omitted or set to 'no', it will not possess any disguise unless it also has a weapon with CanDisguise=yes on the warhead, and uses it on a terrain object.
- Interaction with the PermaDisguise flag needs to be investigated.