I don't understand.
What does "unrecognizable" mean?
What effects/features would it have?
And how/when would it change from "unrecognized" to "recognized"?
The nearest example I can think of is the Faceless alien unit from XCOM2. It starts a terror mision and it looks like a civilian, it acts like a civilian, it's seen by the player and xcom units, but it is not recognized as a hostile alien unit, and definitely it is not a civilian unit.
My idea was to have terrorist unit with an armor in the appereance of a civilian that didn't trigger the red icon when spotted, making use of its looks in order to get near xcom soldiers and kill them with a melee attack or a close range weapon. This way, the player must find visual clues to guess if a civilian is in fact an alien in disguise, and decide if shooting a civilian is worth the risk.
I initially planned to make an alien that directly looked like a civilian, but I soon remembered that it wouldn't matter, as soldiers would recognize it as hostile anyway as soon as they spot it. That is what I meant for "unrecognizable", soldiers simply doesn't react to that unit as soon as they spot it, they don't stop their actions, the red icon doesn't pop up. Not unless that unit is, for example, recognized and forced to revert to its natural alien shape (turning into another unit, just as a zombie creates a new chryssalid).
It can be forced to revert to a normal alien unit by being attacked, or standing too close to another xcom unit. Definitely it is not a unit changing factions, nor a unit that is not an enemy under conditions. It is an enemy, it behaves as an enemy. The playes just doesn't have any certain clue, except the suspiction of that weird civilian alarmingly running straight to his soldiers, or killing other civilians.
I know it is very difficult to understand/believe that something as "small" as this could be so big to implement in the code.
I don't have any good non-technical explanation unfortunately.
You'll just have to believe Stoddard and myself that it is indeed a very big task.
I really don't know how complex it is, and as an amateur gamedev myself, I believe you guys when you say it is. But as far as non-technical explanations go I think this is the closest I can get to my initial proposal. Hope it helps, and if it doesn't, I guess i'll just drop the idea into the bin.