Bethesda games are -far- from the standard when it comes to character customization, and I Can't think of any game that's had mods take care of body-types. It's just too difficult, as it requires much more complex work than most modders are comfortable with--internal animation skeletons at LEAST.
...That said, there is this:
""Okay, let's clear up some confusion! If you pledge to back a henchman you will get to design a character and yes, he or she will have a unique background and dialogue. The difference between them and companions is simply that the story line of companions will be very deep and diverse - like Dragon Commander. There will be a limited number of them because they require very very much work. We can't possible do that for every henchman. But that is where the difference ends. You'll make the guy or girl you like; design their look; their abilities; their build; their background; what they have to say. They will feel like individuals, not puppets, it's just that they won't have separate quests." Apr. 25, 2013 Kickstarter Update"
So there are definitely different characters builds in the game, which means it shouldn't be too hard to implement build customization in for the player proper. Especially considering that the player can create his or her own henchmen in-game, in addition to the two protagonists.
