In our recent combined experimental and theoretical study [Maklar et al., Phys. Rev. Lett. 128, 026406 (2022)], we investigate how a dynamical insulator-to-metal transition affects fundamental interactions, such as electron-electron and electron-phonon scattering. We utilize optical excitation to transiently alter the energy gap of a charge-density-wave compound and observe a concurrent, highly unusual modulation of the relaxation rate of hot quasiparticles. State-of-the-art calculations based on non-equilibrium Green’s functions provide a microscopic view onto the interplay of quasiparticle scattering and the transiently modified electronic band structure, highlighting the critical role of the phase space of electron-electron interaction. Our results vividly demonstrate the possibility of controlling quasiparticle relaxation rates by transiently tuning the electronic band structure using light pulses.