Sorry for the long wait, but I've talked to Baal regarding your question since I'm sure it's something a lot of people would like to know as well and I didn't want to just say something without asking her first. Anyways, it essentially depends on the extent of what you're wanting. We only allow facial/structural edits that affect the 'silhouette' of the head, as in anything outer lying that doesn't need anything behind it to be drawn in. Slightly changing the jaw shape, or perhaps removal of some horns, ect. would be fine because they mostly require just drawing a line and using a layer mask to remove anything that you want to remove. The eyes aren't something we'll edit, but depending on what you're asking for the facial edit it could potentially be done.
Take this male Carapace for example. Baal removed his nasal horn. This only requires adding a layer mask to remove it.
If this is about what you're wanting, this could be done.The only thing I had to draw was a line, and it required no addition of shading or anything. Just a black line and then layer mask to remove anything outside of that line. If you're wanting more added in order to round the face out I can't do that, but yeah. If this example (right side) looks about like what you're wanting, sure.
Edit;
Also, here's an example using one of my own Paragon.
If I wanted to I could get the one on the right done since it's minor and only requires a layer mask.