Creating a MSI patch (.msp) by hand?

Question

Our team has recently been considering pushing out a minor registry fix to users to modify one particular problematic key. Pretty straightforward stuff, just needed to update 1 key/value inside the registry.

So at the moment, we are using Wix to build .msi installers for the product. While looking into Wix's support for generating .msp patch files, it seems that the only way to create an .msp is a somewhat overcomplicated multi-step process to:

1. Get a copy of the original MSI, and compile a new copy of the fixed MSI
2. Write a new Wix file that points to both installers
3. Compile the Wix file into a .wixobj with Candle to a .psp
4. Run Torch/Pyro over before/after snapshots of the original installers and the .psp, or alternatively using MsiMsp.exe

Now my question is, can't I simply describe the registry change into a Wix file and directly compile it into the .msp, without step 1 and 4 - which is a huge amount of effort for just a simple change?

Answer 1

No. A patch is the delta of two installable images. To generate the delta, even if the difference is very small, you will need both images.

Answer 2

It is possible to create MSPs (patches) and MSTs (transforms) using Orca and the other tools from the Windows Install SDK (which is now part of the Windows SDK). However, the process may not be much easier than what you already have with WiX.

Here is the best explanation I could find with a few minutes of Googling; I still suspect there must be something better out there, though. But if you're familiar with the Windows Installer format, it's pretty easy to explore and try a few things with Orca until you have the hang of it.