  Measurements of the mass or angular momentum of a black hole are onerous,
particularly if they have to be frequently repeated, as when one is required to
transform a black hole to prescribed parameters. Irradiating a black hole of
the Kerr-Newman family with scalar or electromagnetic waves provides a way to
drive it to prescribed values of its mass, charge and angular momentum without
the need to repeatedly measure mass or angular momentum throughout the process.
I describe the mechanism, which is based on Zel'dovich-Misner superradiance and
its analog for charged black holes. It represents a possible step in the
development of preparation procedures for quantum black holes.
