This setup does not seem to work on Mac OS. Having followed the above guidance, Bitcoin Core returns the following error on launch:
"Cannot parse configuration file: the options configuration file contains an invalid line '{\rtf\ansi\ansicpg1252\cocoartf1343\cocoasubrtf160'.Only use key=value syntax"
...and then quits out of the launch process.
Answer for those who come after me (thanks to key help from picobit):
The Mac OS text editor is setup to operate with rich text and if one changes the bitcoin file extension to .conf from .rtf it won't change the format of the content, thus generating the above reported error. Thus one must:
1. Set TextEdit for plain text in the New Document pane of TextEdit preferences AND...
2. Open the Save dialog, choose Customize Encoding List from the drop-down menu for Plain-Text Encoding, add Western (ASCII) as an option, and choose that option for saving the bitcoin.conf file in Users//Library/Application Support/Bitcoin
The bitcoin.conf file you create/edit with TextEdit should contain the (ASCII) text suggested by the OP in the first post of this thread.
I have added the relevant information to the how to.