I am trying to edit an XML file with Wix. I am using the WixUtilExtension bundled with Wix 3.7. The xml file is a settings file created in Visual Studio 2010 for a C# applicatio
Yes, this is possible but if you want to have this determined at install time then the preprocessor is not an option. The preprocessor executes during the build process.
To get what you want, you'll need to write another custom action that takes the arbitrarily long set of user data and adds temporary rows to the XmlConfig table. The WcaAddTempRecord() function in src\ca\wcautil\wcawrap.cpp can do the work. The src\ca\wixca\dll\RemoveFoldersEx.cpp is a pretty good example of using WcaAddTempRecord() to add rows to the RemoveFile table. You'll want to do similarly.