If I was Ernest I would configure Kbin to use a key/value map. Of instance name and a bot user id.
If instance request failures reach a threshold it which switch out the user agent to something new for that instance.
Perhaps you randomise it a little, perhaps use the lemmy id, etc..
My goal wouldn't be malicious, more to mess with the lemmy devs. They can be honest an defederate from all kbin instances or spend lots of time quietly blocking them.