It was "sort of" clarified in here https://forum.corvusbelli.com/threads/forming-fireteams-a-summary.3553/page-12#post-238388 I asked, do Wildcards Join or do they Replace. They "sort of" said Replace. They can't replace those that need the Haris or Duo skill though. That troop still needs to be there. The problem is the phrase "can be part of any Fireteam of this Sectorial Army." That wording can mean both Join or Replace. I was looking for concrete Yes and No answers but not getting them.