Indeed, you can't change representation name directly in Table of Contents or disable it.
You give a name to representation when you create it. This name can be changed in Feature Class Properties -> Representations tab (in Catalog window -> right click -> properties).
When you create a legend, however, "Representation: representation_name" can be turned off. Just untick Show Heading and tick Show Layer Name, which is editable in ToC.
Is it what you need?