“The Sims 2: Super Collection is a new, unique product that must be purchased from the Mac App Store,” notes Aspyr. Aspyr media currently has no plans to bring the game to Steam or Origin in the near future. For more information, check out the official FAQ. Buy The Sims 2: Super Collection for $29.99 in the Mac App Store. 
What I've Figured Out So Far I bought it yesterday and had the same question. The game is sold, unfortunately, through the Mac App Store which means it has to be sand-boxed and signed, factors that may make it inhibit modding outside of Aspyr's official package installer, or at least Aspyr's support of it.
However, I've figured out this much. Inside the game, I found a 'Enable Custom Content' setting in the options. (See attached image.) To enable, navigate from any screen that allows you to access the Options menu: Options --> Game Options --> Asterisk (in upper light blue box) --> Enable Custom Content --> Restart the game.
Outside the game, there is The Sims 2 Extras, consisting of Body Shop and Package Installer, downloadable once you sign up for a Aspyr's GameAgent. Read what it says on The Sims 2 Extras page ().
Quote: IMPORTANT NOTICE: 3rd party content (Mods, textures or objects) could corrupt your save game or cause other issues with The Sims 2: Super Collection. Use at your own risk. So, although I have not yet tried it, my guess is that we probably can install custom content, although Aspyr is not providing us with a drop-into-folder method. Instead, if we really must install 3rd party content, we are being asked to use the 'Package Installer' As an aside, I've tried the control-alt(option)-c to enter a debug mode in an attempt to turn off aging. I have not been able to make that work. Read what it says on The Sims 2 Extras page (): So, although I have not yet tried it, my guess is that we probably can install custom content, although Aspyr is not providing us with a drop-into-folder method.
Instead, if we really must install 3rd party content, we are being asked to use the 'Package Installer' As an aside, I've tried the control-alt(option)-c to enter a debug mode in an attempt to turn off aging. I have not been able to make that work. There's a FAQ for The Sims 2 Extras: which gives locations to find saved sims, packaged lots, custom body shop content. It's under Library, which Apple like to hide on recent OS X versions, but it does look like it might be the place to drop all those packages into a downloads folder. The location seems to be: ~/library/Containers/com.aspyr.sims2.appstore/Data/Library/Application Support/Aspyr/The Sims 2/ If someone can check it and find out whether it works, I'd be interested to know the results.
Mac torrent sites. I already have a Bootcamp partition with all the Windows EPs and SPs, but I find I don't take the trouble to reboot and play it as often as I'd like. I'm seriously contemplating sacrificing Free Time and Apartment Life for the trade off of extra convenience and retina support, so if I can get my hacks and custom content in there I shall probably buy it.