Is there a way I can access and edit the Character Controller component's script?

I think the character controller component is a little limited and I want to create my own script to use ase a Character Controller component.
However I don’t want to start from scratch, I thought of getting the script to the Character Controller component that Unity already has and start from there.
Is there a way I can open its code in visual studio and save as a different script?

The CharacterController is not a “script”. It’s not even written in C#. It’s a built-in component and most of its code is written in native C++ code like most of Unity’s built-in components. From the physics system’s point of view the CharacterController is just a stationary CapsuleCollider.

What exactly do you think is “limited” and what exactly would you want to change?