Well, there’s a lot of different ways to go about it. Most people just move the vertices by hand. I once had a script that used the skinning to do it in 3ds back when I used 3ds a lot. It would match the vertices location based on the skin and then morph the other model based on the difference. You could also try using a cage deformer, I’ve heard there’s a way to do it that way but haven’t ever tried it myself. Now days I just do it by hand using things like Flood, soft selection and all that jazz. Honestly though, from a production stand point it’s better to use scaling joints for body customization. Most modern games are using scaling joints now. For instance, FO4, BDO and Skyforge use scaling joints.