Camunda process versioning using "Process Instance Modification" migrate call activities

In our project we have problem with camunda process versioning.
We have read some guides and decided to use Process Instance Modification over Process Instance Migration due to limitations that the last approach has.

So currently I am trying to develop migration framework based on Process Instance Modification.

And first issue I encounter is:

How properly migrate process instance which currently stays on wait point in Call Activity?

For example, I have process:

I start it. One exectuions stays on wait point before Message 1 event. Another gets into Call activity and stays there before message event.

By using Process Instance Modification I stop processes in Call Activity and then start them again (changing variables, and bpmn model to the latest). How can I attach them to the parent process instance which called Call activity in the first place, to make it return back to the parent process instance (which called Call activity) and proceed with processing (executing Task 6). What if I want to migrate parent process as well?
(I found similar question but with no answer yet)