Rob has all the details. Hitting the release candidate milestone — as opposed to the practice run of RC0 — means that the functionality is complete and we’re now only fixing and otherwise triaging bugs. So now’s your chance to get fixes in before attention turns to WiX v3.7 and v4.0.
Is this problem something you guys have fixed in your latest version? How can it not be possible to do this basic operation in a wix installer?
http://windows-installer-xml-wix-toolset.687559.n2.nabble.com/How-to-save-return-code-from-a-command-line-CustomAction-td7579242.html
MSI doesn’t support what you want to do and neither does WiX.