Disable Customized Component Preview

In the constructor of the component, set the Hidden property to True.

C#:
public Component_Name()
  : base("BlahBlahBlah", "Blah", "Life is visceral.", "Cat", "Pan")
  {
    this.Hidden = true;
  }

Link: http://www.grasshopper3d.com/forum/topics/component-disabled-preview