First off, there are 2 locations you need to find on your Mac:
1) the FM installation folder (to apply the real names fix) and
2) your user data folder (to add logos / faces / kits / skins)
To find the FM installation folder is easy.:
> open the Steam client
> go to Library
> right-click (light tap on the trackpad with 2 fingers) on FM & select Properties
> on the new window, go to Local Files tab & click the Browse Local Files button
You will be taken to your FM installation folder that will open on Finder.
To install the real names fix, please follow the instructions on its download page. This fix is for FM17 but will work with FM12 as well, since these license files are essentially text files.
Your user data folder, can be found here:
/Users/[Your Mac Username]/Documents/Sports Interactive/Football Manager 20XX/ (where XX is 12 in your case)
Enter that folder and install the graphics of your choice. That link will take you to FM17 graphics, but they can be used on FM12 as well.
Hope this helps.