It was left out because a)the 3rd level of Mind Trick would have been to powerful compared to other force powers b)you could kill certain units, which would be important for trigger events and the gameflow c)"Force Possession" is full of bugs.
If you possess certain creatures (like ALL reborn, beside the generic yellow reborn, or Luke) the game freezes and kills the PC (at least for a while
That cheat is quite old. If you didn't knew it, these codes might be new for you, too.
NPC SPAWN x y
Create Creature "x" with the name "y"
(Example: NPC SPAWN stormtrooper tk427)
Permanently possess NPC with the name x
(Example: CONTROL tk427)
Return to your original body
Become a member of the enemy team (imperials are your friends now)
Switch back to normal game (imperials are your enemies)
Some imps shoot you, others don't. Starnge.
Like "p" key
Set angle of third-person view to x (180 is frontal view)
Set range of third-person view to x (80 is normal distance)