Apple - How do you disable Siri permanently on macOS Sierra (10.12.6)?

It is not my work but Rich T. has a great post on this at his blog:

https://derflounder.wordpress.com/2016/09/20/blocking-siri-on-macos-sierra/

You will need to deploy two separate configuration profiles, the relevant keys are below:

Domain: com.apple.assistant.support.plist 

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" 
"http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>Assistant Enabled</key>
    <false/>
</dict>
</plist>

and

Domain: com.apple.Siri.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" 
"http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>StatusMenuVisible</key>
    <false/>
    <key>UserHasDeclinedEnable</key>
    <true/>
</dict>
</plist>

Depending on how you manage your macs, and how you want to deploy these profile settings they may need to be constructed differently.

As far as I know these two profiles are the only way to disable this.

Here is a link to the mobileconfig profiles for these settings. You can deploy them with any MDM:

https://github.com/rtrouton/profiles/tree/master/DisableSiri

Otherwise you will need to use defaults write:

defaults write com.apple.Siri StatusMenuVisible -bool false
defaults write com.apple.Siri UserHasDeclinedEnable -bool true
defaults write com.apple.assistant.support 'Assistant Enabled' 0

Once you make these changes you will need to clear the preference cache:

sudo killall -HUP cfprefsd

And then restart the WindowUI server:

sudo killall SystemUIServer

Hope this clarifies.