Ok, so I've had a bit of a play around with the rigs, and I've found out two things:
1) Sims 4 Studio does not import scale key frame information from blender, at least not for the sims rigs. So any adjustments you make to scale in blender will not be carried over to the game.
It is possible to add it again once your in Sims 4 Studio but it would take alot of poking around with values in the Channels section within the Warehouse tab.
2)You can however manipulate the ZYX Translation of a few bones in blender to produce "shorter" limbs, and this is carried over to the game no problem.
To make a sim shorter I'd recomend only really messing with the Thigh bones and the Forearms, select each bone and, making sure your pivot center is set to individual origins, adjust the position of the bone slightly on the Z axis (blue). Moderation has definitely key in my tinkerings, the mesh will soon deform if you push the bones to move too far from their original points. You can also get a shortening effect by moving the spine and pelvis bones on the Z axis, but this did tend to through out the rest of the proportions quite alot.
I haven't found anything that would work for width I'm afraid, but I hope /\this/\ helps and makes sense.
