I was able to successfully edit my CPU name, but had to do it slightly different than Shaneee's tutorial.
1. When mounting the root partition, I got the following error:
$ sudo mount -uw /
mount_apfs: volume could not be mounted: Operation not permitted
mount: / failed with 77
To overcome this, I disabled SIP by editing my EFI config.plist to change the csr-active-config setting to E7030000 in the NVRAM section.
2. My Processors.strings file was not in an XML format like in Shaneee's tutorial. So I couldn't use a text editor (Atom in my case) to edit the file. Instead, I used ProperTree.
Success!
EDIT: After this was all done, I re-enabled SIP by changing the csr-active-config setting in the config.plist back to 00000000.