This can be achieved via executing the following SQL
update relationship_order ro
set role_order = role_new_order.new_role_order
from (select role_createdat_index.target_role_id target_role_id,
role_createdat_index.source_role_id source_role_id,
'sssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssss' || chr(ascii('a') + role_createdat_index.rnum::int - 1) as new_role_order
from (select rst.target_role_id,
rst.source_role_id,
d_right.content::jsonb->'__meta'->>'createdAt' as target_doc_created_at,
row_number() OVER (PARTITION BY rst.source_docref
ORDER BY d_right.content::jsonb->'__meta'->>'createdAt',
rst.target_role_id) AS rnum
from relationship_source_target rst
join relationship_role rr_left on rr_left.id = rst.source_role_id
join document d_right on rst.target_docref = d_right.model_name || '/' || d_right.id
where rst.source_docref in ('YourDM/ids-inserted-here', 'FooDM/1234-5678-90ab', 'BarDM/abcd-abcd-abcd')
) role_createdat_index
) role_new_order where ro.id = role_new_order.source_role_id or ro.id=role_new_order.target_role_id
This uses the view from How to find all documents that are related to a specific one?.
The approach with calculating the new role_order value is limited to a max of 26 elements on the n-side because of the limited size of the supported alphabet for that column value. The relationship_role.id of the target value is used as a secondary ordering criteria to avoid conflicts when documents where created within the same second.
For our application we had to reorder all elements in a multi-hierarchical domain where we could use the transitive_relationship_source_target view also mentioned in that other post. Therefore the where clause
where rst.source_docref in ('YourDM/ids-inserted-here', 'FooDM/1234-5678-90ab', 'BarDM/abcd-abcd-abcd')
needed to be replaced by
where rst.source_docref in (select tr.target_docref
from transitive_relationship_source_target tr
where tr.source_docref in ('YourDM/ids-inserted-here', 'FooDM/1234-5678-90ab', 'BarDM/abcd-abcd-abcd')
union
select unnest(ARRAY['YourDM/ids-inserted-here', 'FooDM/1234-5678-90ab', 'BarDM/abcd-abcd-abcd'])