I followed the instructions in this answer to completely disable the Cortana process... before realising it disables the whole search feature for the start menu.
The answer said to rename Microsoft.Windows.Cortana_cw5n1h2txyewy to Microsoft.Windows.Cortana_cw5n1h2txyewy.bak (add .bak file extension).
I am now stuck on how to resolve this - as I want to use the start menu/Cortana. I have tried removing the .bak, but it mentions file permissions/Trusted Installer. I did try using GrantPerm, but it didn't seem to help the issue.
These are the two Cortana files I can see in C:\Windows\SystemApps:
Just to clarify, Cortana does not open (nothing happens).