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
the rotation axis you want to rotate about, and
-drag
to rotate the joint about the selected axis.
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.