We investigate both theoretically and experimentally a laser-based controlled tuning of the nonlinear behaviors of a single mechanical resonator. Thanks to localized three-dimensional modifications induced by femtosecond-laser irradiation, a Duffing-like oscillator is switched from a hardening resonance to a linear response and then to a softening resonance and exhibits a wide tunability of the resonant frequency and a remarkable increase of its linear dynamic range. The principles that underlie laser-tuned nonlinear oscillators are generic and simple, suggesting its wide applicability not only for micro-or nano-optomechanical systems but also as a generic framework for characterizing and understanding the physics of in-volume laser-affected zones.