What exactly could we do to it that would affect its mass significantly? Ship a significant mass back to earth? If things come to that scale, it can be easily c

What exactly could we do to it that would affect its mass significantly? Ship a significant mass back to earth? If things come to that scale, it can be easily corrected by dropping asteroids on it to balance the mass loss. This sounds like a "we shouldn't have any fusion or fission in space!" argument.