Converting a skin detail to a default skin???

The so-called "default" skins are actually a set of 35 different layers blended together (overlays for fat, muscular...). I'm not sure that this partial overlay would look good on all of those layers. But if you want to try you can open Skininator, create a package with all female overlays, then open this package in Sims4 studio, open Photoshop or a similar software, import each different layer, paste the Cinnamon Roll V2 layer over your exported picture, and re-import in Sims4 Studio.