Hi. Not to worry: (1) The Earth’s orbit is a result of its distance from the Sun and velocity around the Sun — not its mass, although the Earth’s; and (2) the Earth’s mass is so staggeringly large, that if we were to ever significantly change its mass, we would have to be so advanced that we cannot imagine what we would be like or what concerns we might have!

No one is talking about transporting any significant fraction of the mass of the asteroid belt to Earth. The mass of metal that humans use is minuscule compared to the mass of the Earth.

Earth’s mass: 6,000,000,000,000,000,000,000,000 kg.