it is indeed possible, i have them installed myself.

You can download the same pack as PC users, but then just save it in User>Documents>Sports Interactive>FM2013>Graphics

If in doubt most facepacks come with a readme file that tells you how to install it :)

or feel free to ask me any more specific questions
depends if the facepack comes in a rar or zip format, you can get programs to open them on the Mac, not sure which one i use, its all personal preference just google "mac rar zip extractor"