The role of disorder on ferromagnetism has generally been detrimental. We show how Mn-Ni antisite disorder enhances polarization in CeMnNi₄. The disorder is determined to be 6% by x-ray absorption fine structure. The electronic structure of pure CeMnNi₄ is pseudo-half-metallic. Site exchange alters the near neighbor bond parameters and modifies the density of states favorably, increasing the polarization (obtained by first-principles calculations) from 13 to 47% (experimental ~ 66%).