Updates cell values for multiple existing rows in a single bulk operation. Each entry in the request body must include a valid rowId and the columnId–value pairs to modify. Only the specified columns are updated; all other cells remain unchanged. Use this endpoint for batch corrections, data refreshes, or updating cell values. Id columns cannot be updated, but can be included for enrichment purposes if runEnrichment is true. Optionally trigger re-enrichment on the updated rows by setting runEnrichment to true in the request metadata; to limit enrichment to specific columns, provide columnId values in the metadata columns field. This operation is asynchronous. Returns 202 Accepted with a jobId. Poll the Get Bulk Job Status endpoint at GET /v1/audiences/{audienceId}/rows/actions/bulk/job/{jobId} using that jobId to confirm completion. Returns 400 for malformed requests or invalid rowId references.