Replaces a texture png with given command line input

render.py

# Run as: blender -b <filename> -P <this_script> -- <image_path>
# Example: blender -b myfile.blend -P render.py -- new_texture.png

import bpy, sys, os

# Assume the last argument is image path
imagePath = bpy.path.abspath(os.path.join(os.getcwd(), sys.argv[-1]))

if not os.path.exists(imagePath):
    print("Image not found:", imagePath)
    sys.exit(2)

# Change the image data block name to match your blender file
bpy.data.images['foil.png'].filepath = imagePath

# Render to separate file, identified by texture file
imageBaseName = bpy.path.basename(imagePath)
bpy.context.scene.render.filepath = os.path.join(os.getcwd(), 'render-' + imageBaseName)

# Render still image, automatically write to output path
bpy.ops.render.render(write_still=True)