Something

on $*:TEXT:/^[+%@]*/Si:#:{
  if ($left($1,2-) ison $chan) {
    if ($left($1,1) == +) var %option = v
    if ($left($1,1) == @) var %option = o
    else var %option = h
    mode $chan $+(+,%option) $left($1,2-)
  }
  else { halt }
}