This can be edited, but you don't need a mod to do so.
This story can be found in a text file, found in
assets/minecraft/texts/end.txt. Using a resource pack can change the appearance of it, but as far as I am aware, you can change the text to whatever you want simply by re-writing the file.
The Technical Details on the wiki have a bit more information about the text formatting.
If you want to use it for multiplayer games, you will need to make a mod pack and include the file(s) in that mod pack, to be installed in each player's games. You could even change the Credits (found in
assets/minecraft/texts/credits.txt) and add yourself in as a mod creator!