We're working on tools to help you do this. In the mean time, here's something you can try:
Take the skin of your first character (the one the anatomy was modeled for), duplicate it, and project the duplicate onto your new character. You can use something like wrap3, or do it using other tools.
Duplicate the original skin again and convert it to a Ziva bone.
So now we have in the scene three meshes with the same vertex order:
And also some anatomy geometry:
l_bicep, r_bicep, l_humerus, r_humerus etc, etc.
Convert skin_original to a Ziva tissue. Make sure volume conservation is set to 0. Turn poisson's ratio to 0, change the material type on the zTissue from StVK to corotational.
Make a blendshape between skin_projected (target), and skin_bone.
Set two keyframes on the blendshape weight.
Frame 1: set key to 0
Frame 10: set key to 1
If you play back now the bone should travel from the position of the first character to the position of the second character over 10 frames.
A few more steps:
Make an attachment from the tissue to the bone (select the tissue, then the bone, make an attachment)
Now the tissue will follow too.
To make the muscles follow along, you embed them into the tissue.
Select the tissue first, then shift select a mesh that you want to warp, and select Ziva > Embedded Mesh
Playback the simulation and you should see the embedded anatomy shift to the proportions of your new character.
After 15 frames (5 frames to settle) you can delete all your ziva stuff and you have your warped anatomy.
For best results make sure your skin meshes are closed or mostly closed objects.
Make sure you have enough tet resolution to support the changes in curvature.
You can play with the material properties of the tissue too
Oh, turn gravity off! (zSolver node)