  At low temperatures, spinel CuIr$_2$S$_4$ is a charge-ordered spin-dimerized
insulator with triclinic lattice symmetry. We find that x-rays induce a
structural transition in which the local triclinic structure is preserved, but
the average lattice symmetry becomes tetragonal. These structural changes are
accompanied by a thousandfold reduction in the electrical resistivity. The
transition is persistent, but the original state can be restored by thermal
annealing. We argue that x-ray irradiation disorders the lattice dimerization
pattern, producing a state in which the orientation of the dimers is preserved,
but the translational long-range order is destroyed.
