Since the feature is not implemented yet, you can use the below query to update custom status for the notable in Splunk from Phantom.
| makeresults | eval rule_id="<id>", status="<custom status>", comment="<enter comment here>", owner="<owner name>", user="<owner name>" , event_id="<id>", time="<time>" , rule_name="<rule name>", urgency="<urgency>"| table comment event_id owner rule_id rule_name status time urgency user | outputlookup append=true incident_review_lookup
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