  Localization may survive in periodically driven (Floquet) quantum systems,
but is generally unstable for aperiodic drives. In this work, we identify a
hidden conservation law originating from a chiral symmetry in a disordered
spin-1/2 XX chain. This protects indefinitely long-lived localization for
general--even aperiodic--drives. Therefore, rather counter-intuitively, adding
further potential disorder which spoils the conservation law delocalizes the
system, via a controllable parametrically long-lived prethermal regime. This
provides a first example of persistent single-particle `localization without
eigenstates'.
