Not a valid add-on, according to the guidelines.
- Do not overwrite existing add ons, especially the ones included with the game
This means you have to have a unique datablock names and uiNames for all of your stuff.
This overwrites the horse (depending on order of load - if the Super Horse loads first, the Horse will overwrite it). It has a unique uiName, but it uses the same datablocks as the horse.