Preserved german locos that run on the Köln - Aachen line do not have the apropiate destination boards available with the locations of the Köln Aachen stations. (DB BR 422, DB BR 143, DB BR 146, DB BR 766.2 and 767.2)
Matt said they are working on implementing it in one of the HMA release streams. It is now possible because the station destination boards have different end destinations as well.
This is the same on all German route. For example on RRO. The RE trains won't have the correct destination heading away from Hagen. Because they are stock borrowed from MSB
So far the destinations in the trains are hard-coded and come with each route/loco addon. They aspire to let the trains get that information from the route so any train/loco with destination board automatically has the destinations from the respective route.