How to add tags to an existing IAM user via AWS CLI.
aws iam tag-user \ --user-name john.doe \ --tags '{"Key": "Department", "Value": "Accounting"}' |
Multiple tags.
aws iam tag-user \ --user-name john.doe \ --tags '[{"Key": "Department", "Value": "Accounting"},{"Key": "Manager", "Value": "jane.doe"}]' |