Somewhere I have read something about explorators placing the mind of anothor into thier bodies, an in essance having two minds. Does anyone know what I am talking about? I could have sworn I ran across it in one of my books, but I could be wrong.

It's the Rite of Duplessence elite advance from ItS.

Fluff source- Gunheads (Steve Parker), one of the IG novels, set on the ork-held world of Golgotha in the run-up to 3rd Armageddon. The tech-priests who provided the intel for the mission were using the attempt to recapture the lost Baneblade Fortress of Arrogance to recover some secret of their own (can't remember exactly what, been a while since I read it), and had one of their number splice the memory core of the (deceased) magos who supplied them with intel once they recovered it. Said magos then effectively possessed and completely took over the body he was sharing and ran their secret mission from then on…

Thank you! It was the Rite of Duplessence I was thinking about