“Thanks to Sealed System Volume, running this on any file on the /System volume only modifies the file temporarily: It’s reverted on reboot.”
A race condition lets a normal user overwrite read-only files, and Apple’s own XNU source contained the test case. Patch to 13.1 or anyone with a shell can edit what should be locked. The sealed system volume undoes it on reboot. Files on writable volumes stay changed.