As in title, can you elect to spend a regular order on 1 member of a fireteam (not the fireteam leader), kicking them out, but preventing the whole fireteam from activating? e.g a fireteam core in a bad position with multiple potential AROs, but one member is in total cover - can I spend a regular order on that one member, to perform an action, potentially kicking them from the fireteam, but preventing the rest of the fireteam from activating and triggering the AROs? Ideally with the fireteam still intact.
I don’t think you can. I think you’d have to break the fireteam then reform it. You don’t have to spend anything to cancel the fireteam as you can do so voluntarily but you’d then reform the team using a command token.
The "Fireteams in the Active Turn" rule says that "during the Active Turn, Fireteams behave differently from other Infinity Troopers, as explained below," and "During the Active Turn, all the Fireteam members are activated with a single Regular Order from the Order Pool of their Combat Group." This has, from time immemorial, been taken to mean that fireteam members can't be activated individually by regular orders, since they instead "behave differently" in that all fireteam members are activated with a single order. I'm not sure if the origin is an @ijw ruling from years ago, or if it's just a community consensus. The exception is the lieutenant, who can spend her lieutenant order but will be kicked out of the fireteam if she does. This comes from the "Fireteam Integrity" rule which states it explicitly.
I have always wondered about that and thought that in order to voluntarily break a fireteam you have to spend orders to bring into effect a rule that explicitly states that a given trooper leaves the fireteam (i.e. intentionaly move him out of coherency with the team leader). Could you point me to the specific page in the rules where it says that one may cancel a fireteam just like that? I really enjoy using fireteams, but sometimes (for example in the situation described by OP) they are quite clumsy. Usually thats due to bad positioning on my part :D but anyway, I would be interested in the rules that state that you can just do that, and what it "costs" and at what stage in a turn you amy do so.
https://infinitythewiki.com/Fireteam_Cancellation The Fireteam can be cancelled voluntarily by the player, with no expenditure of Orders or Command Tokens. (As a small note, to avoid headaches I suggest you do not cancel fireteams in the middle of orders)
Thank you for pointing me to that link! So bearing this in mind you could theoretically resolve the bad situation described by OP (with the caveat that the fireteam in its entirety will be cancelled, not just the lone trooper leaving it).