Something like "Install OS X Yosemite" will work... until someone renames the installer application to something else. then it won't work. The reason is because the executable isn't called "Install OS X Yosemite". Its called "InstallAssistant". Install OS X Yosemite is the name of the app bundle. So unfortunately, at the moment at least, blocking "InstallAssistant" seems to be the only truly reliable way to stop it from running.
Its unfortunate that it will also stop Mavericks installations, but we actually control that on our managed Macs anyway.
I see it now, but if I click on the "Free" button it tells me "This item is temporarily unavailable. Try again later." Anyone else seeing that? Or is it downloading for everyone else and its just me?
I wanted to d/l to test our Restricted Software process. At the moment, it looks like the App Store is doing a good job of not allowing it to download all by itself. :)
Confirmed success with our Restricted Software in place. The install downloaded, opened automatically and before I clicked on 2 continue buttons it shut down and the Restricted Software message appeared.
So, blocking "InstallAssistant" still works as expected with the final release.
I'll be curious to hear how others are faring with blocking other processes. There's certainly more than one way to do it.
@mm2270 - I confirmed it also. I hadn't put my own Mac into an exception list yet, so when Yosemite finished downloading and tried to run, Casper caught it. Same way, it used the InstallAssistant process to catch it. Has anybody been able to confirm that it can also be blocked by specifying the process as "Install OS X Yosemite"?