Where do I find the NEI configuration file?
Solution 1:
For the mod NEI (NeverEnoughItems), your configuration file can be found here:
%AppData%/Roaming/.minecraft/config/NEI.cfg
or more familiarily: C:/Users/[Your username]/Roaming/.minecraft/config/NEI.cfg
As for adding a lock on cheatmode, simply change this line in the configuration file:
cheatmode=0
Line 22 - Deactivate Cheatmode
lockmode=1
Line 29 - Activating Lockmode
Note: Line numbers may vary from version to version.