As stated here: https://blogs.msdn.microsoft.com/astebner/2006/12/14/some-useful-things-i-have-learned-about-windows-installer-and-uac/
I'm unable to run custom actions with administrative privileges and access to the Session-Data (f.e. to get Registry keys or paths that I need). The only way I can get administrative privileges on my custom-action is by running (Execute-Property of the Action-Call) this action as deferred or on commit instead of immediate.
What I understood by now is this:
Since there is no way to model background-knowledge in the WIX-Install System (like f.e. I want to install a Microsoft Office AddIn) I need to model my background-knowledge by creating procedural C# Code. (Or not?) Why should I not need Administrative privileges then?
Please tell me if I overlooked something. Am I approaching this wrong?