Close. However, you can't just add to n0 or you'll erase the item that was there. Also, you seem to be adding everything twice to the line.

Code:
menu channel { 
  -
  Add # To Favourites:{ writeini $qt($mircini) chanfolder n $+ $ini($qt(mircini),chanfolder,0) # $+ ,,, $+ " $+ $network $+ " | echo -at Some changes might need mIRC to restart to take effect. }
  -
}


That should do it. Also, you shouldn't require a restart for that change.