Hi Luca,
Production Key field is to activate the plugin in live mode.
So if you enable this field, that means that the plugin is active in live mode now.
For disabling the realtime rates in the plugin, you can disable the field “Enable DHL” in plugin settings.
This will allow you to print labels but the rates will not be shown.
If you face any more issues, requesting you to raise a ticket if you are a premium user.