Using the visual editor of Castle Game Engine is always optional. So, yes, you can do everything from code, including loading scenes created in Blender (see https://castle-engine.io/blender ). Follow our manual about using code to manipulate everything, like https://castle-engine.io/viewport_and_scenes_from_code .
Though I should add that I would still advise to test the editor. It's a great tool to easily test the most important components and their properties of the engine. Many things are easier to learn, and then faster to do (and iterate) in editor than limiting yourself to "only code". And then, from code you can always edit 100% of the things that have been visually designed. Even for games where 100% of the content is procedurally generated, the editor remains useful to quickly test everything, design UI etc.
But, it is your choice :)