LH rebooking is usually OK, but only for on the day cancellations, they certainly won't provide it for redemptions booked a long way off. EW has a different ticketing structure so normally that allowance does not extend to EW operated services even when codeshared off from LH. That said, it's just my speculation it's DUS, if it is then Köln would be a good alternative to my mind. But the general point is that specific information gets specific help.