Something to keep in mind here. It's the light that is always going to be diffused. So...
When you create the diffusion effect by placing the diffusing medium over the camera lens when creating the negative, you are causing the highlights (denser areas of the negative) to be softened.
When you try doing the same by placing the diffusing medium over the enlarging lens, you are now causing the shadows (denser areas of the print) to be softened.
Most viewers find the former effect to be often quite pleasing, but the latter effect to be somewhat strange.
Ken
Ken