Thanks for the feedback! The ability to create a tenant will be a part of the initial introduction of API calls that make writes to the database.

As for an XUID on the tenants, I'm assuming you're asking for a generic, user-defined field that you can use to place the unique ID of a tenant from another service you're trying to integrate with. Allowing API calls to specify filters by this XUID would be a great way to potentially reduce necessary API call usage. I'll add this to the backlog.