Hi Peter,
Transition instance IDs are indeed not stable. They are derived from the execution structure as there is no dedicated database field for them (unlike activity instance IDs). With this limitation, I am afraid you cannot implement the feature the way you describe it. I can’t really think of a practicable workaround that works in the general case. Transforming a transition instance into an activity instance like you propose is not possible unless you execute the job successfully.
You could raise a feature request in our JIRA for making transition instance IDs stable.
Cheers,
Thorben