I want to load a material instance inside the Material Editor.

You can’t. But what you can do is use a Draw Material to Render Target node in blueprints. If you draw to a Render Target asset, you can reference it in your Texture Object node. If you use a Create Render Target node, and draw to that, replace the Texture Object with a Texture Object Parameter node in your master material. Then create a dynamic material instance of your master material, and use a Set Texture Parameter Value to reference the Render Target being drawn to.

Is there a way?

It sounds like a lot of work, but it is possible.
Let’s consider.
Thank you for answer.