Hopefully these questions weren't asked many times before. I tried looking on this forum and elsewhere, but didn't find the answer.
When I browse the GFX folder I see three types of files:
.PNG files: Texture files. Very easy to edit with various photo editing programs
.DDS files: Texture files. I've been able to easily edit These with GIMP (after installing a plug-in)
.HKB files: 3D files with the textures added into them? I have been unable to open these with any program.
I have no ambition to edit the 3D assets in the game. However, I do want to re-texture a lot of the items (or rather: add new versions of them for items I invent myself). For example I didn't like that my custom faction had the Krax Spider on their bronze shields, so I created an alternative version with little effort.
Encouraged by that humble first success it got me exited to do more. But I quickly ran into an obstacle. For example I want to add a texture for one of the hats. I found the hat I was looking for in the folder: GFX\HKB\Hair\ K_Male_Hair_Flatcap_Mesh_01.hkb
When I look in the folder I do find the HKB file, but not a DDS or PNG file to edit the texture I am looking to change. Does that mean that the texture is included inside the HKB file and has no seperate texture file? If so, that would be a problem for me as I have no idea how to access those... 
Does anyone know how to "extract" the textures from a HKB file and re-attach them later?