Hi Magnus,
Yes, you can create your own statement GUIDs. They are, in essence, nothing
but the entity ID and a random number.
$guid = $entityId->getSerialization() . '$' . trim( com_create_guid(),
'{}'
);
https://github.com/wmde/WikibaseDataModelServices/blob/master/src/Statement…
https://github.com/wmde/WikibaseDataModelServices/blob/master/src/Statement…
I hope that helps. Sorry, no guarantee, Editing via action=wbeditentity
should always work, but you will probably run into the same issue.
Best
Thiemo