I enjoyed designing a map for Prey a lot, because of the great atmosphere and unique features that no other game has.
It is really sad that the game lost its popularity so quickly, it definitely deserves a better fate. I'd gladly play some more custom maps for it.
prevent Tommy from ever being immortal (instead being dead for real when killed, as it happens in the first parts of Prey) -- but still allow him to use his special ability
I think it will be that way if you give item_spiritwalk to the player, but don't specify the deathwalk map in your map def file.