You can rotate joints while using the Paint Skin Weights Tool. This lets you test the way joints deform the bound geometry as you paint skin weights.
To rotate your joints while using the Paint Skin Weights Tool

 -click
               to switch from the Paint Skin Weights Tool brush
               to the Rotation manipulator.
 -click
               to switch from the Paint Skin Weights Tool brush
               to the Rotation manipulator.
 -click
               the rotation axis you want to rotate about, and
 -click
               the rotation axis you want to rotate about, and   -drag
               to rotate the joint about the selected axis.
 -drag
               to rotate the joint about the selected axis.
 and
  and   arrow
               keys to select other joints up or down the joint hierarchy. For
               example, walking up the joint hierarchy to LeftArm (shoulder) or
               down the hierarchy to LeftForeArmRoll.
  arrow
               keys to select other joints up or down the joint hierarchy. For
               example, walking up the joint hierarchy to LeftArm (shoulder) or
               down the hierarchy to LeftForeArmRoll.