Disable Narrator shortcut key in Windows

I have not tried it personally but here's what I found.

1. Navigate to %systemroot%\System32
2. In this folder a file called Narrator.exe is to be found
3. Right click the file and choose Properties
4. Choose the Security tab and press Advanced
5. In the top of the window press Change to change the Owner permissions
6. In the text field write your username and press OK to all the dialogs

Now you should be able to change the permissions of the file, this is where we remove all the permissions from your user and change the owner back to SYSTESM; this way your user will not be able to start the Narrator.

1. Right-click the Narrator file again and choose Properties and Security
2. Press Advanced
3. Now that you are the owner you can change permissions for other users. Choose your own user and press Edit
4. Remove the Read & Execute and Read permissions and press OK
5. Now press Change in the top under Owner and write system in the text field
6. Press OK to all dialogs

Source

If you're familiar with editing the Windows registry, you can use the solution described here:

• Launch regedit.exe and navigate to: HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options
• Create a key with the name Narrator.exe
• Inside the key, create a new String value called Debugger, and set its value to %1

This won't be changed by Windows updates, and can be easily reverted by just deleting the key.

If you don't use any Windows Assistive Technology features, you may also want to create a registry key for AtBroker.exe with an identifical string to prevent it to be launched as a rogue process in the background every time you accidently use the Narrator shortcut.

Pressing the Capslock and the Esc keys at the same time brings up a window that allows you to Exit the Narrator.