If you want to change all the regular deckers to cyber deckers, just change them in characters.xtbl to use the cyber decker npc model. For example, change this:
into this:
Just change the <character> entry for whichever decker npc you want to use the cyber decker character model. As for using avatars as specialists- can't be done, none of that giant avatar stuff works properly outside of the mission for now. To make a gang of zombies, just apply the zombie flag (try and find it yourself!) to whichever character you want to act like a zombie.