Hi!

All content classes have a method called GetIconUrl that you can override. Then you have full control over the icon urls that is returned. 

So you need to create a content class in Webnodes that inherits from ContentFile, override GetIconUrl and set the replace class dropdown of the class you are inheriting to ContentFile. If some of the file extensions you want to customize is not using ContentFile, but ImageFile, VideoFile etc, you need to create additional classes that inherit from them, where you also override GetIconUrl.

Vidar