We show that the ferromagnetic anisotropy of a thin crystalline Fe3O4 film can be manipulated in situ via the application of tunable stress. The stress is exerted by a piezoelectric actuator, onto which the Fe3O4 film is cemented. The strain in the sample is quantified as a function of the voltage applied to the actuator using high-resolution x-ray diffraction, and the corresponding evolution of the magnetic anisotropy is determined by ferromagnetic resonance spectroscopy. By this means, we are able to directly correlate structural and magnetic properties. The experimental results demonstrate that a piezoelectric actuator allows to substantially modify the magnetic anisotropy of a crystalline ferromagnetic thin film, enabling a voltage control of magnetization orientation. The possibility to orient the main elongation axis of the actuator along any given direction in the film plane opens a pathway for the investigation of the magnetoelastic properties of ferromagnetic thin films under tunable stress, shear, or combinations of both stress and shear.