OK, I think I'm going at this wrong - here's another angle. I assume it's fair enough to say that you believe in Flying Pig, and that you believe that he's an English bloke, who used to be a soldier, who posts on CFC and has an interest in history. If you got a PM from someone on this site who had dug up the secrets of my past and found that I'd actually been a ballet dancer, you might say something like 'Flying Pig wasn't a soldier; he was a ballet dancer', but you wouldn't doubt my 'existence'. If, on the other hand, you found out that the person writing my posts was actually an author creating a fictional character, you might say 'Flying Pig doesn't exist'. What, though, if the author was actually writing an autobiographical character? You might fairly give either response - either 'Flying Pig doesn't exist, but John Smith the author does, who is like him', or 'Flying Pig exists, but he's actually an author called John Smith'.
So do we say 'Jesus existed, but he was actually not as we're told', or 'Jesus didn't exist - the person who really did is a separate entity'?