When I export the game, I need a way to add Actors (it can be while the game is "Paused"). This can be done through some sort of pop-up interface or through some other way; I'm open to ideas.

It won't be possible while the scenario is paused, but you can manually program it. Maybe with your own pause button. If you click it, all actors freeze and some other buttons appear. If you click a button, a new object of the desired class is added to the world and is (maybe) following your mouse until you click into the world or something like that. Of course you can also do it without stopping the rest of the scenario. You could divide the world into two parts. The world in which the actors are acting and some buttons which can be used like explained above.

It would be possible to set a different world active and use my PIP Actor Class to create a mock instance of the actual world inside that world. You can code in the outer world the actions for adding objects into the inner world and then, upon exiting, you can return to the actual world. The inner world will remain in a paused for the duration (unless you use any of the calls that allow it to be in a visually active state). Just an idea. For another demonstration of the PIP Actor class in use, check out my World Scaling Demo scenario. In fact, that version of the class might be more useful (if I did not update the other one).