User blog comment:Sergeant Michael/Crossing over/@comment-1009967-20131106024103

Well, I can tell you that it's been done before, both right and wrong. Just take one look at SpecOps306's Xenomorph article for an example of how it's done right. On the other hand, my own abandoned project Halo: AVS: A Worthy Foe ought to be deleted, but I've gifted it to another user who doesn't seem to be around and should probably be deleted anyway.

Case in point, it's possible. The trick is doing it right, and you'd have to be very careful in execution. Make it so that it's the Halo universe, just with Xenomorphs or Yautja added in, in an isolated case so it doesn't have universe-wide repercussions that would necessitate canon to be broken. But overall, I'd recommend not making the attempt and instead dedicate your time and energy to something wholly Halo.