You are able to do this using a Group Policy.

open gpedit.msc

navigate to Computer Configuration > Administrative Templates > Windows Components > Windows Defender

Turn off Windows Defender = Enabled

more info:

http://aaron-hoffman.blogspot.com/2015/08/install-and-setup-windows-10-for.html

and http://www.download3k.com/articles/How-to-Turn-Off-Windows-Defender-Permanently-in-Windows-10-01350

You are able to do this using a Group Policy.

open gpedit.msc

navigate to Computer Configuration > Administrative Templates > Windows Components > Windows Defender

Turn off Windows Defender = Enabled

If you then try to open Windows Defender you'll see this:

And even though in Settings it may appear to be on, the Service is not running:

more info:

http://aaron-hoffman.blogspot.com/2015/08/install-and-setup-windows-10-for.html

and http://www.download3k.com/articles/How-to-Turn-Off-Windows-Defender-Permanently-in-Windows-10-01350