I have script that I start from scriptrunner console or by Automation manual action.
I do not understand why value in custom field is stored, but there is no update event, so new value is not seen from Structure or there is no line in issue's history about this change
finish.updateValue(null, issueObject, modifiedValue, new DefaultIssueChangeHolder())
So I see new value on issue screen, and if open edit screen. But some additional update process is needed.