You've got your Mac and your Steam games and they're awesome, but you also want to put your saved Steam games over to a new hard drive without having to download multiple gigabytes of data. So the question is as follows: What's the best way to go about this? Read on to find out!
The good news: All your Steam games reside in one folder on your hard drive and it's pretty easy to get to Head to ~/Library/Application Support/Steam and copy this folder into the same location on your new hard drive.
Ok, you're going to be waiting a while for your Steam files to copy over to the new drive (in my case, I moved over 50 gigabytes of data to an external hard drive prior to installing the files to the ~/Library/Application Support/Steam folder on my MacBook). Use this time to your advantage and get the basic Steam app up and running on the hard drive you're setting up.
To do this, simply go to the Steam download link, snag the Steam installer for Mac OS X and install the file while your Steam games copy over.
After copying is finished, all you have to do is copy the files into place. Installing Steam for Mac OS X will have created a set of Steam support files, so tell your Mac to replace them if the dialog box asks you to.
After copying the files over, launch Steam and you'll then be prompted for authorization. Choose the second option ("What email message? I don't have it...") to have Steam email you an authentication code.
Once the authentication code has arrived, copy and paste it into the dialog box, click "Next" and Steam will authenticate the new computer.
From here, you're home free. Just choose the the game you want to play from your Steam library and begin playing as you normally would.
And that's really about it. Even though your hardware profile HAS changed to a certain degree with the new hard drive, Steam is tolerant of this and will verify you after you put in the new authentication code. So, without further ado, copy the files over to the Mac you want to play on, authenticate it and you'll be able to play every Steam game you ever purchased and downloaded.
