Okay, so I'm making a rig and i need to redo the automatic weights on the hands, but already went and hand weight painted the face and the face and everything is perfect. If i parent the mesh with automatic weights to only the bones in the hand, it still redoes all of my weight painting in the face (the entire body is one mesh). So is there any way to only assign new weights to a certain area or bones without redoing the entire thing? The only way i thought of doing it another way is to separate the mesh of the hands and re parent that.... i also am asking specifically about using automatic weights, i know how to use empty groups, just wondering if there was a faster work around. thx.
Another method is: select the armature, shift select the mesh, go to weight paint mode, using control left click select a bone, go to menu, weights, "Assign automatic from bones".
Anothed faster method is: use padlock icon to lock all the vertex groups you want to leave unchanghed, then perform a new automatic weights parenting.
Mark the hands with a vertex group (we'll call it "dtHands".) Duplicate your mesh. Autoweight your duplicate. Give your original a data transfer modifier, targeting the duplicate, copying vertex groups on the basis of topology, limited by dtHands vertex group. Hit "generate data layers" button as necessary. Test deforms, possibly smooth out the border of dtHands group to make a more even transition. Apply the data transfer modifier then delete the duplicate.