@Rellwood:
As the ToolTips say, it only protects manual editing using Edit Metadata. It does not protect anything else, including Search and Replace and Standard Calibre manipulations.
The ToolTips also mention that other plug-ins may need those custom columns unprotected.
Ignore the ToolTips at your peril.
Purging the .json, uninstalling JS, etc. does nothing. Waste of time. The metadata.db table that is updated to reflect the 'editable' value (0 or 1) is table custom_columns.
Use JS to un-protect what you previously protected.
Or, if you want to use
http://sqlitebrowser.org/ to manually edit table custom_columns in metadata.db, be sure to make a back up of metadata.db first.
DaltonST