Any Vegetarians/Vegans here?

[StoryBook]

So what make a carnivore a carnivore and herbivore a herbivore?

Before I answer your other points lets address this. Do you think I could theoretically feed a herbivore a diet based on meat alone yet it still be healthy? I can tell you that I could.

How could I do this?

I see that it is clear that you don't know then. If you did you would not of asked a silly question.
A herbivore can not stay healthy on a carnivore diet, the same as a carnivore can not stay healthy on a herbivore diet.