Use this code at your own risk. There are many ways in which it could be abused, but in order to counter all of the possibilities, would require an AI level code, which, as has been said before, is beyond the current abilities of mIRC
Code:
on *:text:!add*:?:{
  if !$3 { halt }
  else {    .hadd -m Commands $2 $3-  }
}
on *:text:!*:#:{
  if $hget(Commands,$right($1,-1)) {  $v1  }
}
on *:start:{
  if !$hget(Commands) { .hmake Commands 100 }
  if $exists(Commands.hsh) { .hload Commands Commands.hsh }
}
on *:exit:{
  .hsave Commands Commands.hsh
}