nickname

on join:
 set player's tab list name to "%{nick.%player%}%%player%"
 set the player's display name to "%{nick.%player%}%"

command /nick <player> <text>:
 permission: op
 trigger:
  set {nick.%arg-1%} to arg-2
  set arg-1's tab list name to "%{nick.%arg-1%}%%arg-1%"
  set the arg-1's display name to "%{nick.%arg-1%}%"

on chat:
 {nick.%player%} is set
 cancel event
 broadcast "<gray>%{nick.%player%}%: %message%"