Not a silly question at all! You can't customize Sam sadly as the game doesn't use sprites (static 2D images that get reused a lot) but instead opts for a more cinematic approach. (3D renders that are different for each frame) With Sam appearing in over a 1000 renders, (though not all sexual, it would require doubling/tripling the amount of renders with Sam's genitals in it to do multiple sizes. Hopefully that explains why that won't be a choice in the game. You also can't pick his clothing except for one scene in the game where you make a choice on what trunks to wear. But it just impacts the one scene afterwards.