It is OK for Alfred Hitchcock to appear in his own movies. It is not OK for him to create an unauthorized sequel to someone ELSE's movie and insert himself as a new main character that is smarter/stronger/faster/prettier/sexier/more more more better than every other character from the original storyline.

Mary Sue stories are typically fan-fiction.

It is OK to want to be the princess at the ball. It is OK to throw your own ball just so you can be the princess. But it is just stupid to crash someone else's ball and demand they hand over the tiara.

Doc