Does anybody know where or how to change the texture of the robots (protectrons/security bots)? I didn't find any tutorials dedicated to this problem. Also didn't find any mod that has changed textures of the robots.

Regards.
A.

You make a copy of the meshes of the robot, and apply your new texture directly to the meshes. You can then select your new meshes from the robots 'Model List' tab.
But, you have to keep the new robot parts in the same folder as the original, so just rename them.

Thank you so much! I must be stupid or something...

Not really. Most items you can just retexure right in the GECK. But robots you can't.