This happens naturally in the form of meteors streaking through the sky. Each one of those is adding a tiny amount of mass to the planet.
But you’ve got me wondering about something now. When a large asteroid hits the planet, it obviously adds its own mass, but it also kicks up a lot of debris into space. Some percentage of that will reach orbital escape velocity and never come back. But I honestly don’t know if there is a net mass increase or decrease after such an event? We’re generally concerned about other more pressing matters in such a scenario!