A rock could be affected by weathering or erosion. Both processes involve the rock getting changed physically in some form of fashion, but still being the same form of rock.
In order for a rock to be not classified as the same form of rock, its chemical components would have to be changed. This has not occurred during erosion or weathering.
So once more for clarification, a rock can be changed by weathering or erosion but still be classified as the same form of rock.