Current State:

For some time, the API endpoint to Bulk manage customers' detail field values mentioned in this doc
was available for both AAIDs and for portal only Customer IDs. But right now, this endppiint only accepts Customer IDs (portal only customers) and not customers having Atlassian Account.
 

Proposed Future State:

Please extend Bulk manage customers' detail field values to customers having Atlassian account

Alternative (e.g. Third Party Plugin):

N/A