  We explore the possibility of probing flavor violations in the charged-lepton
sector by means of high-luminosity lepton-photon and electron-muon collisions,
by inverting initial and final states in a variety of decay channels presently
used to bound such violations. In particular, we analyse the resonant lepton,
$\gamma\, \ell \to \ell^{\prime}$, and neutral-meson, $e^- \mu ^+ \to
\phi,\eta,\pi^0\!$, scattering channels, whose cross sections are critically
dependent on the colliding-beams energy spread, being particularly demanding in
the case of leptonic processes. For these processes, we compute upper bounds to
the cross-section corresponding to present limits on the inverse decay channel
rates. In order to circumvent the beam energy spread limitations we extend the
analysis to processes in which a photon accompanies the resonance in the final
state, compensating the off-shellness effects by radiative return. These
processes might be studied at future facilities with moderate energies, in case
lepton-photon and electron-muon collisions with sufficiently high luminosity
will be available.
