How to open (decompile?) and replace textures.
What you need:
WinRar
Star Citizen Texture Converter (goo.gl/o4gZ4R)
Photoshop/GIMP with .dds and .tif plug ins
 
Before doing anything backup your /data/ folder (or atleast the .pak files you want to edit) just in case

1. Navigate to "/kingdomcome install folder/data/"
2. Open the .pak file that contains the textures you want to edit (in this case i opened heads.pak)
3. The files that are named *_diff.* seem to be the actual texture files, the other ones seem to be overlays or something
4. Extract the textures you want to edit to a new folder (in this case its bernard_diff.x)
5. Rename *_diff.dds to *_diff.dds.0  
5a. If you are editing overlays also rename *_xxxxx.a to *_xxxxx.0a
6. Extract the Star Citizen Texture Converter to the same new folder and run sctexconv_1.3.exe
7. It should extract the textures and now you should see *_diff.tif in the folder
8. Open this file in photoshop/gimp and edit it how you please
9. After finishing save the file as *_diff.dds
10. Open the .pak file you originally extracted the textures from again
11. Delete all the files you originally extracted (in this case bernard_diff.x)
12. Add the texture you edited (x.dds) by draging the new .dds file to the winrar window and wait for it to pack
13. Go to /data/_fastload/
14. Open the packs here and see if the texture is stored here also, if it is repeat steps 11-12
 
also since KG:D seems to use a similar modded version as star citizen, if anyone who is skilled in model editing is interested, on their website i found a guide on how to convert cryengine (cfg ?) model files to ones usable by bender and other 3d editing programs, it might be a long shot but if anyone wants to give it a go here is the thread (https://goo.gl/Qi95n3)