How do I upgrade without adding files with WiX?

Question

I'm making MSI's with WiX for our product. The product loads some optional assemblies as modules. This allows us to just drop a dll into the directory and charge a bit more!

Now I want to make a common major upgrade MSI that includes all the possile module assemblies but only upgrades files that exist, and doesnt install missing ones. How can I achieve this?

Answer 1

Ideally those "drop-in" assemblies should have been installed with another MSI. That way you just need to chain a series of MSIs to do upgrades.