I have a Fahrkarte SPARPREIS EUROPA from London St. Pancras to Frankfurt with change in Brux-Mi., bought through a travel agent from DB Vertrieb GmbH. The ticket is attached to a Kundenbeleg that describes the seat number and reservation, but the ticket itself does not give this information, and the Kundenbeleg is in German. According to Mark Smith posting on Tripadvisor, this is not a problem and the ticket will be accepted. No problem there. However, normally I change my seat to choose a seat I prefer. Is this possible when the Eurostar ticket was issues by DB?
Unfortunately, my understanding is that the answer is no.
Changing Eurostar seats after booking
The only rail operator who permits a seat change after booking is Eurostar.
While there is nothing to lose by contacting Eurostar directly, Loco2 sell both types of ticket and I would expect their analysis to be correct.
I agree with Mark Perryman's answer: as far as I know, this is impossible online. However, I have succeeded in getting my seat changed when checking in at the counter with my DB ticket. Of course the choice will be much more limited at this stage, and it may be completely impossible if the train's fully booked. But it's worth trying, especially if you're after some general category (‘window’, ‘near a door’, ‘near the buffet’, etc.) rather than one exact seat. In my case it was ‘My companion and I booked separately, but is there any way you could seat us together?’.