Installed similar update in my x86 home premium with biosmod. No untoward incident and nothing abnormal happened after installation till now.
kb947821 isn't actually an update, it just has the same nameing convention as if it were an update! Its a repair tool that fixes corruption (or incorrect information) in the windows servicing store, as explained in the product information. It is safe to run and is probably a good idea to, just in case there is a problem found! kb947821 came out a month ago for Windows 7, it has probably already been installed on most computers through Windows update. If not! and it does not show in Windowsupdate, that just proves that there is an issue with your Windowsupdate! You can run kb947821 as many times as you like, even though after the first time it would be pointless unless something happens, the option is there.
This is wrong! Microsoft: This article describes the System Update Readiness Tool for Windows Vista-based computers, for Windows Server 2008-based computers, for Windows Server 2008 R2-based computers, and for Windows 7-based computers. Microsoft released the System Update Readiness Tool to resolve certain conditions that could cause installing updates and other software not to work. You do not have to manually run this tool. This tool is offered automatically through Windows Update to computers that have a condition that the tool could resolve.
You right, I tried to run the standalone installer for this KB a month ago and receive the message that it is not applicable to my system, in other words, the issue is not in place at my computer. This tool will appear at WU if you have the problem.
If you are running the correct version of the tool for your system, you should be able to run it regardless of whether you need to or not. I have seen it run a few times on a straight clean installation of a recent Vista retail (thats the Vista version of the tool of course) and on a clean installation of OEM Windows 7 on a different computer. In every case it has run. Whether the computer is affected by the problem or not the worse thing that it can do is nothing! If its the case that it shouldn't run on any computers and only on those that have a problem, then it is a bug in Windows.