Several times I need to work simultaneously to more than one projects, for example right now I need to copy some classes to an older project and update the code to make it work. The best way as I see it, would be to open multiple projects instead of just one, on the same UI, and switch between them with just one click at the top of the right panel. Then, only the right panel (and the settings) should have to be updated, since on the left panel you can view and work with multiple, different files already. Of course, switching to each project you should be able to build it and run it normally.

You can more or less do that by switching the project from the main toolbar's projects dropdown.