Is it possible to inject dynamic legal hold metadata into Agent Scripting API payloads?

Is it possible to append custom metadata fields, specifically legal_hold_id and chain_of_custody_ref, to the JSON payload when triggering a bulk export via the Agent Scripting API? Current documentation lacks examples for custom attributes. The standard request below returns a 200, but the resulting S3 manifest omits these keys, breaking our audit trail validation.

{
 "export_type": "bulk",
 "filters": {"date_from": "2023-10-01"},
 "metadata": {
 "legal_hold_id": "LH-992",
 "chain_of_custody_ref": "CC-441"
 }
}