Adding a Hero to DotA

[Entitymaul]

Hey guys!

I'm on campus at the moment and for our project, we've been asked to mod a game. Straight away, the first thing I thought about was adding a hero to DotA. So, what's the go on that?

I'm thinking of using a pre 6.60 map. Maybe something like 6.49 or something that's still not as security tight as the current versions.

Would it be hard?

Is there a chance I can just modify a hero? I know I can modify the name and the backstory of a hero, but can I modify spells and/or spell damage? Or even just changing the hero's model. Is that hard?