Find MSI install package for pre-installed application?

Here's what I'm looking to do:

I'd like to perform an application install on a remote machine; as a part of that process, before I install the new version, I want to check that machine's registry for a pre-existing version of the same application.

If that machine has an existing instance of the application already installed, I want to find the MSI used to install it, so I can backup the MSI and perform a 'rollback' if necessary. From what I understand, Windows creates a copy of these MSIs and places them in some temp folder with a random name somewhere so that it can use it for uninstalls.

How might I find this location? (Also, suggestions on how to check the registry values cross-network would be apprec开发者_JS百科iated.)

As far as I understand, you don't have to find the exact MSI package. In order to uninstall a product, it is enough to know its product code and run msiexec /x {PRODUCT-CODE-GUID-HERE}. And product codes can be found under Uninstall registry key (typically, SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall).