First off, lighting is cheap. If VoxelShadowsDisabled is implemented, it probably won’t be for performance reasons.
CFrame should be one of the fastest properties to set because it doesn’t cause a recluster. It might cause some kind of physics update, but have you checked the microprofiler?
do this instead
part.CFrame, part.Size, part.CFrame = part.CFrame, newSize, CFrame.new(3.4e38, 3.4e38, 3.4e38)