Köln Hbf omitted In early October? What to do for transfer?

I would choose one of the other options that does not involve a transfer in Koln.

Right now there is nothing you need to do. October is far away.

As the message literally says: Please check for changes to your journey prior to departure.
Schedule changes happen. Currently there is one direct train per hour from Köln Ehrenfeld to Düsseldorf, and a few with a change, so no worries.

But why did you not book one of the direct Eurostars?

(Note that "Please check for changes to your journey prior to departure" is something you should always do. Train tickets are for a route, not a train, and it is very common that if you book tickets far in advance you will not end up traveling according to the schedule you selected during booking. Yet another reason not to jump the gun on train tickets...

Thanks, travel4fun and WengenK,
The Eurostar option turns out unavailable for the day and the following day. It is grayed out on ES calendar. So I assume there is a construction or some sort being planned. I will see if this changes later with my finger crossed.
And thanks for the information about frequency of local trains. This is my first time for planning trip with DB.

Although I have not personally travelled between Dusseldorf and Koln, I have been to both. They are so close and inter-related that it is reasonable to assume that at the absolute worse, you will have to take a temporary bus between them. I would not stress about this in the meantime.

However, Koln does have a well-deserved reputation for being easily explored (by other travelers, not mentioned in your itinerary) on foot from the HBF. So this is a warning for shoulder-season visitors who take a daytrip to Koln in October, 2024.

You can also transfer at Aachen Hbf to the RE 1 or RE 4 direct to Duesseldorf Hbf, which bypasses Koeln altogether. It gets to Duesseldorf a bit later than the planned itinerary, but eliminates your worry. Since you can take any RE direct to Duesseldorf, you could spend an hour or two in Aachen if you like.

Thank you, Tim and Sam!
Thank you for sharing your valuable tips. Bus availability and the idea of transfer at Aachen are kinds of I could only get from those who are familiar with trains and the area, which I am very much thankful to you both. I will look into them. This community rocks!

You are here seeing a bit the difference in philosophy between railways that use NRT ticketing, and that use IRT ticketing.

IRT tickets are "tickets for a train", so you can not start selling tickets until you are 100% certain your train will run. Eurostar does this. So does Trenitalia, RENFE, SNCF. That leads to sometimes tickets only becoming available at the last moment. This is probably why you can't book the direct train yet.

NRT tickets are "tickets for a route". As long as a railway is not planning on completely discontinuing a route they can sell tickets. DB does this. They assume (correctly) that train service to Düsseldorf will not suddenly cease. So they sell you a ticket for the route from Brussel to Düsseldorf, and can do so even if they are not sure what the schedule will be.

Both approaches have their pro's and cons. In your case you have two options:

• Wait a bit till Euorstar starts selling tickets for that route. A direct train is going to be more comfortable than changing. I would expect that late August, or early September you should be able to book.

• Book now with DB. This allows you to take advantage of the very cheap supersaver tickets still available. Then on october 3 check the schedule. Just leave on the same train (because of your reservation) but assume that you may be up to half an hour later.