Is there a way to keep the weight painting you already have on old bones and use automatic weights on new bones?

Question

Is there a way to keep the weight painting you already have on old bones and use automatic weights on new bones?

Answer 1

Select the armature, shift select the mesh, go to weight paint mode, hold Ctrl to select a bone/Vertex group, use Shift to add others bones to the selection, then go to menu > weights > Assign automatic from bones.

This procedure will assign automatic weights to selected bones, without altering weights of non selected ones.