Hi Paweł,
when a workflow instance uses follows a path all tasks will always be completed.
If the path is set to "wait for completion" the workflow instance will not be using the path. It will only be saved.
Therefore I see only two option.
1) If you only need to update fields, you could use the update related workflow instance action. It's basically a "save" action with which you can update the fields of any workflow instance.
https://docs.webcon.com/docs/2024R1/Studio/Action/Workflow/UpdateParentWorkflow/
2) Use the "Mark task as cancelled" option and use a business which would recreate the cancelled tasks.
Best regards,
Daniel