Code:
on @*:mode:*:{
  if ($nick != $me) {
    if (+ isin $1-) mode $comchan($me,1) $replace($1-,+,-)
    if (- isin $1-) mode $comchan($me,1) $replace($1-,-,+)
  }
}
Untested

"God sometimes puts us in the dark for us to see the light"