Is it possible to write a bot, which can only be added by participants of a Tentant, or only in conversations with the participants of a Tentants? A bot, e.g. Data from business applications should not be available to others :-)
On the sandbox the apps are by default not restricted to your tenant. But once you apply for an app on the production system it will be restricted to your tenant by default.
If you'd like to change the sandbox app you have to be limited to your tenant, let me know and we can change that.