Use Effect controls/Rotation to rotate a clip, but that will only show up in the program monitor, not in the source monitor. You can't change the rotation of the source material, since PR is a non-destructive editor.

Actually it makes perfect sense, because you do not want to mess with the original material, only with the edited material. If you want to see modified 'source material' you have to export first and take the generation loss in stride.

Import, rotate, export and then import the exported material is the only way.

The way Pr is set up is that you see your unaltered video in the Source Monitor.  Any editing, including transforms and effects, is done in the timeline and the result appears in the Program Monitor.

Pr is a non-destructive editor; your source files are never altered in any way.  The only way to make your edits in Pr permanent is to export the timeline to a new file.

That said, if you would like the Source Monitor to have more functionality, then please file a request here:

Adobe - Feature Request/Bug Report Form

-Jeff

NB: Personal and antagonistic comments have been removed from this thread.

I come from an audio background

That explains why there's a bit of confusion.  Most audio editors immediately affect the original file.

Pr and most other video editing programs store editing operations and commands in the project file, and apply those operations only when you *export*.  So when you save the file in a DAW, you actually overwrite the original audio file.  When you save your Pr project, you're only saving the list of commands.  You have to *export* to get a file on your hard drive that contains the processed video.  It is a separate file from the original video file, and that original file remains unchanged.

If it helps, think of the Source Monitor as a video player, much like Windows Media Player.  In general, you don't edit or alter the video that you're watching in WMP.  Ditto for the video in the Source Monitor. 

-Jeff