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How to edit system files on macOS

Prerequisites

Preparing the USB Drive

The only way to edit system files, also with SIP disabled, is making it from a macOS USB installer.

You need to have a macOS installer to make a macOS USB; it's not necessary to have the latest macOS on the USB drive.

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Booting from the USB Drive

To boot from the USB drive, restart your Mac and hold down the Option (⌥) key while it boots up. This will bring up the Startup Manager, where you can select the USB drive as the boot device.

Once you've selected the USB drive, your Mac will boot into the macOS installer. From there, you can go to Utilities -> Terminal to make the necessary changes to the system files.