I looked around on google for a while and came across the following method; there may also be a reference or two to this on this very website in the Discussions section (no, I didn't have the foresight to keep the links for the software used on hand).
I used AssetStudio.net6.v0.16.21 to help identify PathID of the image texture file responsible for the gobbos in the data.unity3d file.
Then I used UABEA to export the texture file as a png, erased the gobbos' parts with GIMP to preserve the alpha layer, and then imported the edited file back into the data.unity3d file with UABEA.
That said, even if I went back in and removed the textures for the gobbos' shadows as well the left breast would still be nipple-less.
I'm not familiar enough with Unity to know if painstakingly copying and moving the nipple textures over the left breast would be effective, and I'm not obsessed enough with this product to find out.