You cannot do these with all security enabled, no. There are lots of other things that are prevented by SIP and/or Secure Boot. One of the principles is that being root should not mean that the kernel can be readily attacked without further bugs.
That also means no /dev/kmem etc., and on top of that POSIX file permissions are by far not the only thing that is protecting access to the file system.
That also means no /dev/kmem etc., and on top of that POSIX file permissions are by far not the only thing that is protecting access to the file system.
If you want to go down the rabbit hole: https://help.apple.com/pdf/security/en_US/apple-platform-sec...