Is there any way in the editor to edit textures on the 3d models, or the models themselves, faces for example or is there a free external program that can be used for this?
Short answer yes! (now not the time to collect all links and make longer descriptions):
Use Norbyte's pak extracter tool. Extract Materials. Use search function for finding textures. Get to know the different texture types in the PBR workflow. Edit the textures (preferably with photoshop and intel or nvidia dds plugin). For testing by overwriting the original texture it is easier to save the texture.dds in the game folser in just the same path of the original texture as in the unpaked files. ( you have to create the pass manually)
Or you copy paste the material in resource manager, import the textures as new assets and associate them to your copied material. Copy the head model and associate with new texture)
That now was from my mobile device out of the head and memory. Let's see if i can give you further details. ( or somebody else )
See the wiki aswell.