I designed the KCOPs and own the Kafka Target engine. You are able to pass serializer properties to the serializer being used inside the KCOP (see the docs for putting serializer.property.XXX in the KCOP properties file). Where XXX is the property you want the serializer to be initialized with.

Now the property you probably want to try is auto.register.schemas=false as per the confluent documentation. If you prefix that with the above and put it in the KCOp properties file, we then pass it to the serializer when we instantiate it.

Let me know if it works for you, if not open a ticket.