ME2 question about characters in mission dialogues.?

I've seen a couple videos where people used a save thing on PCs in order to get late-game characters such as Thane or Samara with them on earlier missions, and the characters will actually have input during the discussions. Does this mean the developers foresaw people messing with the game and put in dialogue for those characters (which seems like a reward) or is there a legitimate way to get late-game characters into earlier missions? Importing an earlier Shep into a new game wouldn't let you keep squadmates, would it?