Migration of suspended process

Hi everyone!
Beg for your advice.
Have the following case: about 20k active processes need to be migrated to new definition version.
As definitions differ a lot migration is through java api.
I planned following steps of migration:

  1. Suspend all active processes that must be migrated.
  2. Add new variables
  3. Execute migration plan
  4. Modify processes. As definitions differ, not all activities of previous version have similar activities in new version. But as migration instruction validates only same type activity mapping, I first map to some new activity type in migrating instruction and after migration finished I will move token manually to other activity. I.e. if need map from old timer wait event to new service task.
  5. Activate suspended processes.
    On step #3 I receive ‘SuspendedEntityInteractionException: ENGINE-03043 Execution with id ‘xxx’ is suspended.’ in both sync or async migration execution.
    The problem is that I need process instance modification after migrating to make it run without errors.
    How can I suspend the process instance until migration and modification is finished?