Unique Altdorf
This mod is now also included in the combined version.
This mod adds a unique settlement skin for Altdorf, which changes and grows based on the settlement level. Each settlement level adds some new features to the city. For example, the first level starts with a small village with the temple of Sigmar. The second level expands the city, and the fifth level adds the colleges of magic and the imperial palace.

I’m working on a tutorial at the moment, which I plan to upload as soon as possible. I’ve released this mod mostly as a proof of concept, to show that it is possible.
All of the unique faction capitals could receive custom skins which vary based on the settlement level and the faction that occupies the settlement. For reference, these are the faction capitals:
Non-unique settlements can also get unique skins, but that would require editing the startpos file. Without editing the startpos it would still be possible to change the default settlements, but you would be changing all of the generic ones at the same time.
I’m planning on making faction specific versions of each settlement level, if there would be enough interest in that. That will probably take a while though, because there is a total of nearly seventy possible variations.
Making a custom settlement like this is a -lot- of work. A big part of why it takes so much time is that you can’t actually see the campaign map when you’re working on the settlement. That means that in order to check how it actually looks & whether buildings are in the right spot, you have to export, edit, and then load a campaign.
If there is enough interest I might therefore make this part of the GCCM project (though not part of the same mod) so that we can bundle the work of multiple people into a settlement overhaul.
Edit: It appears there may perhaps be some interest.
Naggarond teaser: https://i.imgur.com/CheYuHJ.gifv
That being said, GCCM has a patreon these days, which you can find here:
https://www.patreon.com/GCCM.
This mod is now also included in the combined version.