While I was making my Autopsy scar mod work with top scar mods, I ended up with these files and these layers that I made from scratch. They aren't perfect, especially since some races seem to have slightly different pec shapes, but I hope they help! I don't care what you do with these in your mods, I am here to remova all unwanted booba.

Example screenshots are from my Autopsy Scar mod, since that's what I was making them for.

Instructions:

1. Pick your version, one for body 2/4 or for the Transmasc Top Surgery mod.
2. Open files.
3. Copy the red channel of your texture to the indicated layer in the document. (You may have to resize if it's scaled up or down.)
4. Enable only that layer and the two boobs above it. (they are separated so you can move them apart if you need for whatever reason)
5. Select all, copy merged.
6. Paste in the red layer on your texture.
7. Repeat for each color channel.
8. Do the same thing with the normal map and normal map alpha.

The idea is that we are converting the color and alpha channels into normal layers to make them easier to work with, then we are pasting the result back into the original channels.

If you are using the Transmasc Top Surgery mod version, it needs a little more work to flatten the boobs. There will also be a "boob flattener" layer for all of the channels except for the normal map alpha. You may need to edit it depending on how your textures look, but at the very least, it shows you how the flattened boob should look. They use the normie textures.

If you wanted a version for Transmasc Top Surgery without the scars, you could also look at the boob flattener layers without the scar layers.

**NOTES TO ADJUST THE FINAL APPEARANCE:**Since these are on different layers, it's relatively easy to adjust the results to your liking. If it is too dark overall for your liking, you can lower the transparency.
Finer adjustments are more complicated, but here's a short summary. HMVY stands for Hemoglobin, Melanin, Veins, Yellowing. That's the redness, the darkness, the blueness, and the yellowing of the skin. Each color channel controls one of these things, in that order. RGBA = HMVY. This means you can darken the R to make it redder, the M to make it darker without making it bluer or redder, and the B to make it bluer. You can also lighten any one of these things or play with the transparency. If you want more texture to the scar, for it to be more raised, then you adjust the normal map.
Because of how skin colors work, some skin colors make redness an entirely different color. This can drastically change how the scar looks. You may have to experiment on your desired skintone to get a look you like.
If all else fails, changing only the normal map apparently works very good on drow-like skintones!