@richchichester The packs can't be disabled, but you can simply move their folders, and they won't launch. In either Applications or Users > your username > Applications, you'll see a Sims 3.app and a "The Sims 3 Packs" folder. Inside the Packs folder is a folder for each expansion or stuff pack you've installed. They're named by type and release order, e.g. World Adventures was the first expansion released, so its folder is EP01.
If you move the folders for the packs you don't want to use out of the Packs folder, Origin won't recognize them as installed, and their content won't load. When you want to use those packs again, simply put their folders back.
