Here's my take (supports both nickmodes and channel modes):

on @*:input:#:{ 
  if ($regex($1,/^[+-][ $nickmode ]/x)) {
    if ($2 !ison $chan) { echo 4 User $qt($2) is not currently on the channel. }
    else { mode $chan $1- }
  }
  elseif ($regex($1,/^[+-][ $remove($chanmodes,$chr(44)) ]/x)) { mode $chan $1- }
}