Editing Metahuman Skeleton ?

Hello,

I just created a custom Metahuman by importing my own geometries (head+body).

After assembly I realised I needed to change the position of the joints, especially head, neck and Elbows. I started making changes on a copy of the Skeletal Mesh and moved around a few bones. Problem is when accepting the changes the mesh is getting deformed when I would only like the joints to move (and kind of reapply the skin post tweak).
Any idea how to achieve this ?

Thanks in advance !

Matt