Unity 2D have come a long way from last release, but it still it is not customizable like Unity 3D.
You can do basic customization with Unity-2D Settings tool.
You can do more customization if you edit some source files.
Problem with this is that changes that you made are not permanent and they will be changed to default with new Unity 3D updates.
Problem with this is that changes that you made are not permanent and they will be changed to default with new Unity 3D updates.