I just made another experiment. I've have a stack of four images, the raw image, processed in LR4, a TIF in which I did some cloning, a VC of the TIF, which I've named sp, and a softproof VC of the VC of the TIF, whose copy name is the name of the profile. Here is what I did.
1. Select the softproof VC. Enter the Develop module and select softproofing, then select side-by-side. The Before copy says Master Copy.
2. Open the Before drop-down list. It shows four choices, saved state (there is none), master copy, the VC of the TIF (indicated by its copy name), and the softproof VC (also indicated by its copy name.)
3. Select the the VC of the TIF as the before copy. The softproof copy is on the right, the image that was the base for the softproof VC on the left.
4. Move some sliders, in this case, HSL saturation and see the changes to the right-side image.
5. Turn off softproof and enter single image mode and see the changes made in the sliders.
So, I think that I have edited the softproof VC.
When my printer is usable again, I'll print both and look for differences.
I hope this helps.