I'm not sure if this came up before but since it's all about the Cadmus I'm not sure it did. Let's say a cadmus succeeded at a combat jump, deploying behind a parapet on a rooftop, while in a seed-embryo state it is in total cover, but if it stood up as an S2 trooper it would be in LoF of a reactive trooper. the question is, when declaring a Move and going prone, is there a moment in which the reactive trooper would see the S2 of a cadmus? It seems that the developed shape profile would apply for the entire order sequence and provide an aro to any trooper that would see its S2, but I'm not a 100% sure on this, and even so there might be a way around it, but first some rules quotes. From the seed-embryo state: The player will replace the Camouflage Marker or Seed-Embryo Token (SEED-EMBRYO) with the corresponding Model when: They perform any Skill with the Movement Label as the first Short Skill of the Order, or Entire Order. The new Developed Form profile is applied for the entire Order Sequence. They perform a successful Dodge ARO. The new Developed Form Troop Profile is applied before making any Dodge movement. And from Prone state: Note that a Trooper that was in LoF before going Prone will still count as being in LoF at the start of the Skill or ARO. If I understand correctly, declaring Move as the first part of the order would retroactively make Cadmus use its developed shape profile and it would gave been seen by a reactive trooper wen declaring its first short skill. But I think there is a way around it, since the profile change only happens if you declare Move as a first short skill, what about declaring a BS attack with chest mines first, and declaring Move as a second skill? The Cadmus-seed would obviously not move, but it would be able to go Prone, and there does not seem to be anything in the rules prohibiting declaring Move and going Prone for a trooper without a MOV value in its profile, so dropping behind a short wall and switching to the developed profile without standing up seems possible, just a bit convoluted. If I missed anything be sure to tell me, but I do hope at least the trick with going prone as a second short skill works as I described.
Note the part where there’s no rule allowing you to convert if you declare Move as the second skill, according to what you wrote.
Of course, I probably didn't get my point across clearly, the idea is that after landing you would spend one order declaring any non-movement Short skill+Move to go prone while steel using seed embryo profile, and then spend another order decaring Move+any other skill to change to a developed shape without standing up as a full S2, I played cadums at a couple of tournaments recently and having access to a cheap combat jump trooper which lands as a 25x3mm SX is very useful, it's a lot easier to find a safe spot to land a 25mm base compared to a full S2, and spending an extra order to change to a full cadmus profile without standing up is a very good way to avoid potential aro's if you landed it behind a parapet. The best case scenario is dropping on a rooftop behind someone with low PH, and ideally blasting them in the back with double shot chest mines stacking -3 for surprise attack and -3 for out of LoF dodge, and if after that you can crawl somewhere with a boarding shotgun and trade cadmus for 1-2 more models, or maybe take a red fury instead, though with BS11 you really need to find a good target for morpho-scan to reliably win shooting face to face rolls.
But why, though? The rules for Unconscious directly specify that "Cancelling the Unconscious state automatically cancels the Prone state." As far as I'm aware there was no issue with deploying a seed-soldier prone to not automatically give away that it is in fact a seed-soldier and not another camo trooper in a prone state, and seed-embryo only changes the profile that the trooper uses, without any mention of interacting with states.
It is a good question and opens for more questions like if states carry over and if wounds carry over, and it is something I never wondered about...
Well it's still the same trooper, it just has two profiles, so all states and wounds should carry over from one profile to another just like with bikers and transmutation(auto).
Looks like the initial post is correct as far as the rules are concerned. It's a similar situation to the strangely mobile AI Beacons. Nothing's preventing BS Attack and then Move to get the embryo to go prone, other than the fact that it is fairly wasteful use of orders. As an aside, this is the only way to use a Seed-Soldier's Surprise Attack skill since the developed form does not have that skill.