Unless you're going to completely redefine and change how techniques are executed, completely redefine forms, and completely redefine sparring, calling something "American Tae Kwon Do" or whatever is impossible. Every once in a while it happens. Modern TKD is much different than the way it was practiced 40-50 years ago. But the changes it has experienced have been initiated and carried out by Korean-born Instructors. I cannot think of one American-born Instructor who has redefined Tae Kwon Do so much it merits being called "American Tae Kwon Do". Anyway, if an American redefined Tae Kwon Do that much, it would no longer be Tae Kwon Do.
Any changes in a so-called American system tend to be more cosmetic or the result of adding other styles. It is still Tae Kwon Do with less emphasis on etiquette, more BJJ or other styles, fancier uniforms etc.
And very few people have the ability to redefine a style to the point where it is now something else but just as good:
Ueshiba, Parker, Won Kuk Lee, and Gen. Choi come to mind.