I have found a solution to toggle the display of a contextual submenu (eg: nicklist,channel).

Code:
alias -l enamnu { .enable #mnu | .timer 1 0 .disable #mnu }

menu nicklist,channel {
  $iif( (test if submenu should be displayed) ,$enamnu)
}

#mnu off
menu nicklist,channel {
  Submenu name
  .$submenu(...)
  ...
}
#mnu end


It works perfectly. The reason to do this is to prevent mirc from calling the $submenu alias which is time consuming in this particular case.

Do you see any disadvantage in using enable/disable?