Hi Stefan,
1. After hierarchy breaking, you will be able to modify this Job, but once hierarchy will be created back, then this Job be managed by Parent again.
2. Hierarchy Editable Properties (HEP) are available for policies but aren't applied for Tasks/Jobs.
3. You can clone existing replicated Job on Child NS (which is managed by Parent NS), then it will be possible to modify it.
Note: If you will clone a job with tasks, then it will clone existing Job as well as all included there tasks!
Thanks,
IP.