Yeah freeze does that in some application such as Maya or Max where it is the action to 'lock' the object while in some others,such as SI|3d or Xsi, it's the term used for the action of clearing the transform history of a 3d object...
Anyways,modeling over the locked object may be a good idea,in fact that's how Steed does it using splines though,but ultimately,you'll want to model those clothes and hair or other accessories WITHOUT any rference except for proportions...The model becomes MUCH more interesting and personalized this way.
Modeling Tip of the Week:Keep away from the infamous frog dissection pose!