Mac Terminal change PDF author

A better way would be to make use of exiftool, which on Mac you could install with use of Homebrew:

brew install exiftool

You would then edit your metadata in your PDF in the following manner:

exiftool  -Title="Change This Title" -Subject="Fun and PDF" change_my_meta.pdf

Removing metadata

If you only want to remove metadata you can use pdf-redact-tools:

pdf-redact-tools --sanitize untrusted.pdf

You could use Automator. I dont think that sed is going to work because pdfs are largely binary, or very jumbled at the least. One of the defined 'pdf' actions in Automator is defining metadata, one field which is author. Then call the automator workflow with terminal, or just save the workflow as a droplet.

For more detail see the screenshot below: