Disable Actor selection in editor mode?

As far as I know this functionality is still missing in the editor. What you can do for now is to Lock Actor Movement so that noone will move it inside editor (in the World Outliner right click on the object → TransformLock Actor Movement). You can use it together with hiding objects on the scene (eye icons in the World Outliner).

It’s not exactly what you wanted but maybe it will help a bit.