I want to convert some field names, not values or data types. I already have schemas registered, how do I use the schema registry so I don't have to paste the literal schemas into the input and output schema properties?
ConvertAvroSchema came before the record-based processors and the Schema Registry. You can use JoltTransformRecord for this, there is an example field name conversion in this HCC answer. If you share your schemas and field name mappings, I can help create a Jolt spec.