Code:
menu nicklist {
  $iif(# == #mpot,A-Voice Control)
  .Shitlist Nick:write shitlist.mrc $$1 yes
  .Unshitlist Nick:{
    if ($read(shitlist.mrc, s, $$1) == yes) { write -dl $+ $readn shitlist.mrc | echo -a Unshitlisted Nickname. }
    else echo -a Nickname is not shitlisted.
  }
}

Or you could use menu styles
Code:
menu nicklist {
  $iif(# == #mpot,A-Voice Control)
  .$iif($read(shitlist.mrc, s, $$1) == yes,$style(2)) Shitlist $$1:write shitlist.mrc $$1 yes
  .$iif($read(shitlist.mrc, s, $$1) == yes,$style(1),$style(2)) Unshitlist $$1:write -ds $+ $1 shitlist.mrc
}