Guesswhoitis gave a nice solution to this problem on the comments above:
LatticeData[lattice, "Image"] /. Sphere[cents_, r_] :> Sphere[cents, 2 r]
Specifically, I did
LatticeData["SimpleCubic", "Image"] /. Sphere[cents_, r_] -> Ball[cents, 24 r]

(I also transformed spheres to balls here). It works because if you take a look at the InputForm[] of LatticeData[lattice, "Image"], it's something like this:
Graphics3D[
{ GraphicsComplex[{{-1, -1, -1}, {-1, -1, 1}, {-1, 1, -1}, {-1, 1, 1}, {1, -1, -1}, {1, -1, 1}, {1, 1, -1}, {1, 1, 1}},
{ EdgeForm[GrayLevel[0.8]], Opacity[0.1], Polygon[{{8, 4, 2, 6}, {8, 6, 5, 7}, {8, 7, 3, 4}, {4, 3, 1, 2},
{1, 3, 7, 5}, {2, 1, 5, 6}}]}],
{ GrayLevel[0], Specularity[GrayLevel[1], 5],
{ Sphere[{-1, -1, -1}, 1.44], Sphere[{-1, -1, 1}, 1.44], Sphere[{-1, 1, -1}, 1.44],
Sphere[{-1, 1, 1}, 1.44], Sphere[{1, -1, -1}, 1.44], Sphere[{1, -1, 1}, 1.44],
Sphere[{1, 1, -1}, 1.44], Sphere[{1, 1, 1}, 1.44]}}},
Boxed -> False, ViewPoint -> {4, 5/3, 1}
]
And you can transform the spheres, manipulating their radii and positions.
LatticeData[lattice, "Image"] /. Sphere[cents_, r_] :> Sphere[cents, 2 r]might work. – J. M.'s missing motivation May 26 '15 at 03:59InputForm[LatticeData[(* stuff *)]]to see what it's made of, and you should be able to figure out why the dilation replacement did what it did. – J. M.'s missing motivation Jun 08 '15 at 04:22