Unable to spoof MacOS level in order to install printer driver for Canon i950

I booted into single user mode (CMD + s). As the first attempt failed due to insufficient authority to edit the SystemVersion.plist, I tried again using su to switch to root, but this didn't allow me to edit the file either:- su: Sorry apfs_vfsop_mount:1171 Updating mount from /dev/disk1s5 to read/write mode is not allowed mount: / failed with 77 I was trying to edit SystemVersion.plist to change Product(User)VisibleVersion to 10.5.0 or later as expected by the Canon driver installer (I'm actually on 10.15.7).

Question by John Nicholson on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.