Change is reverted on M1 after exiting temp shell and reboot

[sbogun]

I have followed the whole procedure on my M1 running Monterey 12.4:

• compiled writeable_root.c
• disabled File Vault
• booted into Recovery Mode
• csrutil disable
• csrutil authenticated-root disable
• rebooted
• executed ./writeable-root
• modified /System/Library/Automator/Combine PDF Pages.action/Contents/Resources/join.py (it is buggy)
• exited the shell

After the following reboot the change is gone and the contents of the file reverted. How come?

I don't know whether this is the same problem as described in #3 (that's not very verbose :-)).