Seeing if I have this right: Since TAGs are not (normally) spec ops, you can only link one Civ with CivEvac. However, if you dismount the TAG and use the pilot, you can have up to 2. Pretty sure I've got it thus far. Does a pilot get to keep them if they re-enter their TAG, or does one of them "fall off" because the pilot mounting the TAG makes it lose the "Spec Ops" skill, effectively?
Hard to say. By the core rules, there is no limit to how many civilian you can sync, and therefore there is no cancellation clause that if you change your profile from a specialist to a non-specialist that you lose a civilian. So going by the scenario, there are two special rules about how many you can synch. Technically, it did not modify the cancellation clause. And we know from past FAQ that you cannot cancel a state without that cancellation being listed in the cancellation clauses. Specifically, you cannot end your camo state by simply turning it off, not even by activating another NFB skill like Mimetism. Applying the same logic, you cannot simply end the CivEvac state by deciding to not be a specialist, not even by changing to your not-a-specialist profile. (At least you are allowed to spend a Short Skill to cancel the state.) Edit: we also know from previous ITS FAQ that if you can become a Datatracker (being a TAG), and that you stop from being able to be one (becoming a REM), you can still continue being a Datatracker. I would not be surprised then that if you can synch 2, and you did synch 2, you'll still have them when you go back to being a TAG (I mean, neither Civ will fall-off).
Looking at the wording for Rescue, it's pretty clear: "In this scenario, Specialist Troops can have up to two Civilians in CivEvac state at the same time. Other troops able to declare Synchronize Civilian can have only one Civilian in such state." My emphasis. Note that it's not a restriction on being able to declare CivEvac, but on how many Civilians you can have in the CivEvac state at once. A TAG is not a Specialist Troop, so "can have only one Civilian in such state".