How can I add a button to my project that would call a method while not running (runtime)

Questions & Answers
1

How would I be able to run a method without running my project? Lets say I want to populate a area randomly with AI by pressing a button in the inspector or scene.
I know about this: https://unity3d.com/learn/tutorials/modules/intermediate/editor/building-custom-inspector
But would that give me the ability to generate things in the scene as well?

I would like to be able to edit scenes and let my artists generate content without starting and stopping scenes?
This also lets them populate an area with AI and do some minor tweaks.

2

Yes, you can absolutely create assets and gameObjects in the scene without being in play-mode. You can test this by just trying to add a button that does a simple creation of a cube game object, you should see that object appear in your scene. You can also instantiate prefabs, clone objects, just about everything you need to make helpful editor tools.