Kendra Custom field mappings

Unfortunately, we are unable to edit the data type of an existing field after it is created. We can create another custom field but it has to be with a different field name. If that doesn't work for you, you'll have to create a new index.

Yes you can, and it's possible. You can enrich document metadata and content during the document ingestion process using Document Enrichment. This feature enables you to create, modify, or delete document metadata and content when you ingest your documents into Amazon Kendra. Please go to this page for step by step guide: https://aws.amazon.com/blogs/machine-learning/enrich-your-content-and-metadata-to-enhance-your-search-experience-with-custom-document-enrichment-in-amazon-kendra so no need to create a new index.