Can I play through the whole singleplayer campaign using only Tostada?

[NatP]

And if I can, does anything special at all happen? Or does the game just treat me as if I was still Juan?

[Papaya]

Nothing special, every character still thinks you are Juan.

[Fangelstien]

allthough it is funnier because you're refered to as a man, when your clearly not :')

[WillBits]

You have to play through the tutorial as Juan, but once you get to your first savepoint you can switch to Tostada or any skin you've unlocked or downloaded! Some of the unlockable skins sometimes have slightly different gameplay mechanices, but most of them are just for fun. :)