i have a configured Mosquitto MQTT broker...
I'd like to kick or ban a user for an amount of time?
How can i do this from another subscribed client? Should i do this from the broker? How?
You can't block on a client id basis, the only option would be to enable ACLs with a database back end (something like https://github.com/jpmens/mosquitto-auth-plug) and then update the database to remove access to topics to specific users.