How can I copy weights to another mesh which has another rig? Assume I have two identical spheres. I add a rig to the first sphere, then I deform second sphere in sculpt mode without adding new polygons or vertexes. I duplicate the rig and I want to connect this secod rig with my second sphere that the rig could animate this deformed sphere exatly like another rig animates first sphere. Another words I need to transfer weights from the first sphere to the second sphere. But 'weight transfer' option only works with objects that connected to the same rig. So I have two spheres and two rigs.

How can I manage that?
You can copy vertex groups (and corresponding weights) from your first sphere to your second one :


Select second one first
Then select first one
Use "Copy Vertex Group to Selected"



If deformation bones have same names in both Armature, it will work. 
Else, you need to rename your Vertex groups to fit deformation bone names.