Set Application.ActiveProject

Hello,

I wonder if it is possible to set the Application.ActiveProject? Or the selected item like in Application.Selection. The reason is that I have an old custom C# macro that I need to run automatically from the root and the macro tries to access the Application.ActiveProject but it is null becauese the tree is selected in the root above all projects. I know which project I want to set to active but not how.

Regards
Henrik