You can mirror smooth skin weights, either from one smooth skin object to another, or within the same smooth skin object. You can also mirror skin weights on selected components of the skin.
For best results when mirroring smooth skin weights, note the following:
-click and select Control Vertex or Vertex. Select the components on the side from which you want to mirror and the components on the side to be mirrored to.
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Reflection is disabled for the Paint Skin Weights Tool. Skin > Edit Smooth Skin > Mirror Skin Weights can be used as an alternative method to reflect skin weights.