Does anyone have any idea how to change the default data directory on a Mac?
Just put the files in the default location:
~/Library/Application Support/Bitcoin
The tilde (~) represents the root directory of your home folder. The full path would look something like:
/Users/username/Library/Application Support/Bitcoin
If you wanted to change the default location, one way would be to use a symlink. I had to do this for the iMovie data directory years ago:
http://tinyapps.org/blog/mac/200805230700_change_imovie_save_directory.html