Use the Submaterials Tool and Invisible texture Addon to make all textures besides the mask invisible. From there, use the Easy Bonemerge Tool to apply the desired body to the head. THIS IS NOT GUARANTEED.

If you run into issues with the ragdoll, then simply go vise-versa and apply the head to the body. This does prevent you from changing its facial expressions, however, so animators are flat outta luck on that side.

If neither work, then I am sorry to have wasted your time :(

Links to mods in order:

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=405793043&searchtext=submaterial

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=576040807&searchtext=invisible+material

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=170917418