Hey there. I’m not sure if you can change the exact geometry of a physics asset at runtime, but you can do some tricks with the existing geometry. Most of them are not available in blueprints, though. In C++, a skeletal mesh has a “Bodies” array of FBodyInstance*. Each Body Instance has plenty of methods, e.g.
UpdateBodyScale(const FVector& InScale3D, bool bForceUpdate)
directly changes the scale of the shape in 3D, I believe it is what you need, but once again, it’s not exposed to blueprints and will hardly ever be.