I played the demo missions a very long time ago, and I remember having a lot of fun using the different stances (prone, crouch, etc.) back then. I don't think any mod exist that includes them, but I think that would be (kind of) simple to do.
As they use only a pre-generated squad, I would recommend adding them by including a bunch of "simulation" terminals to the first bunker, and launch the missions after the player interact (talk) with them. With some luck (I say that because I never actually tried this), the engine will allow the player main squad to not spawn in those missions and be replaced by the pregenerated squad, and allow for safely going back to the bunker to the original squad (by safely, I mean without the game thinking the game is over because the main character is dead). This would only serve as a lore/immersion type of mission, as the XP and items gained by those characters would stay with them, but this would be easy to flag a campaign variable to true after a mission is completed and use it back in the bunker to add some XP to the main squad for the trouble of completing the mission.
The mod might require to remove and hide the temporary squad members after coming back to the bunker, because I believe they will "follow" the player back to the bunker. I would attempt to remove them BEFORE leaving the misson, but the game might think this is a Game over. Those new squad members might even mess with who is the main player character... So, a lot of tests are in order.
As the Tactics missions give A LOT of XP after each completed mission, like TONS (they use that as the main way to make you reach the needed level for the next mission), I think that adding a couple thousands XP for those missions would not impact the game progression much, except in the very early portion of the game.
As Endocore's Redux mod is of a very high quality and very fun to play (a kind of hardcore experience that I went through twice), I would recommend including those missions to it. One of these days, I would like to go back to Redux mod and update most of its new sprites, so maybe I could attempt to add the demo versions at that time? But he, no promises here of course.
