I’ve also encountered this issue, for exactly the same use-case: attempting to set a different URL for an existing Wizard.
The other use-case is to duplicate a Wizard as a shortcut to developing a new one which shares similar functionality.
The Custom Wizard Plugin doesn’t provide either of these functions in the UI, but it would be very helpful if it did.
Likewise, it would also be helpful if a non-compliant ID was captured when attempting to import the .json so that a corrupt Wizard never makes it into the database. I’m no dev, but I’m guessing that this would be easier to implement.
If you’d like to remove the corrupt Wizard from your instance, you can do so via the Rails console (be careful):
PluginStoreRow.where(plugin_name: 'custom_wizard',key: '=faultyID=').destroy_all