As discussed on Mac Geek Gab 343, it’s useful for many users to re-download the Lion installer from the Mac App Store in order to create a flash drive installer or simply to have a backup in case of a system failure.
Unfortunately, by default the App Store prevents users from downloading software that is already installed on the Mac. The “Install” button in the store is replaced by a grayed-out “Installed,” which the user can’t select.
Thankfully, there is a workaround to this limitation that will allow users to re-download the Lion installer if they so choose.
The default Lion Product Page, showing Lion’s installed status.
Open the Mac App Store and navigate to “Purchases.” Find the entry in your purchased software list for OS X Lion. Hold the Option key and click on the Lion icon to load Lion’s product page.
The Lion Product Page while holding the Option key.
You’ll notice that under the Lion icon, it now says “Install” instead of “Installed.” While continuing to hold Option, click on “Install” and the installer will begin to download.
Once downloaded, move the installer from your Applications folder and store it in a safe place for future use.