Convert Materials from Cycles to Blender Internal Render I want to use Freestyle for a scene with lots of different Cycles Materials, is there an easy way to change them all at once to Blender Internal? 

It would be nice if the materials are somehow related, but thats not that important. More important is, that if one material is used for two objects, afterwards the relation stays the same, having the material assigned to the objects as before and not to others (therefor just assigning one new bi material to all objects wouldnt work).

I know that switching the renderer to bi and unchecking "Use Nodes" in the material tab makes roughly what I want, but doing that manualy for every material one by one takes lots of time. 

Is there a command or script that I can use?
Try running this in the text editor:

import bpy

for mat in bpy.data.materials:
    mat.use_nodes = False


It will disable use nodes for every material.