By no means an expert at this point, I've certainly picked up much information and tricks that permit modding Mass Effect 3 meshes successfully. I am currently revisiting some of my earliest mods so I can correct minor issues in them that I had no idea, then, how to fix. The Ashley Romance Mod is a case in point. It was perhaps the 2nd mod I ever did for the game in which I made the Ashley romance scene more mature and fitting an adult-minded player. I made her body much less like that of Marilyn Monroe and much more like her original body (a model from Athleta women's exercise clothes magazines). I also made her topless because I was insulted that they had her in a bra and panties...even upon waking the next morning after it was clear that sex happened. What woman does that?! Leaves ON her bra during sex OR even worse, puts it back on afterward and sleeps in it? They should have handled the whole thing along the lines of Mass Effect 1. Nothing blatant but CLEARLY showing that sex was happening and that the participants were, correctly and realistically, nude. Kinda like you see in any prime time TV show (in the US) or soap opera.
The main problem I had with the mod turned out to be the normal map. I kept thinking it was the mesh or the difference texture or the spec, never thinking it was the normal which, in any case, I had NO idea how to deal with back then. I had used a Gimp plugin to generate a new normal map for the revamped difference texture but it just didn't work. Paint.Net also doesn't do any better in that regard. I then tried CrazyBump and it was better/closer but still not right. Rather than spend days and days trying different settings with Crazybump to see if it will EVER produce a usable/working normal map for the Unreal 3 game engine of ME3, I futzed with trying to find a way to be able to edit normal maps in Gimp. I stumbled on the working format for this: u888. The normals come out of the game as v8u8 but Gimp (and Paint.Net) cannot handle this. Using Nvidia utility nvdxt, I finally converted the v8u8 to u8888 and that was closer but then I realized I didn't need the alpha layer...there isn't one in the original, so I tried u888 and viola! Perfect! Gimp can import it fine, it presents as you would hope and expect, you can edit it, save it , and then reconvert it with nvdxt to v8u8 and put it back into the game. Best of all, it works as well as the original. Finally a way to use the normal maps from the game with my mods that sometimes actually require the normal map be changed. The Ashley Romance Mod was THE postergirl for this need. Now she's 98% fixed. Download it, install it, enjoy it. I hope to improve it in the near future.