There is a tool that should perfectly do what you want: LgpCli on GitHub.
It has two modi:
a) find, inspect and set policy (like GPEdit) this can also help to create the commandline
b) commandline - just use this in your script to set the policy

so your final command would be:

LgpCli disable wuau.AutoUpdateCfg Machine

There is also a page that should explain how policies work: Policies Description

Disclaimer: I'm the author of that tool, however it is not commercial, free to use and open source.