You can't change bone selection during skin painting, but this sample macro script shows you how to bind a macro to a hotkey to improve your skin weight painting workflow.
MacroScript SkinPaintModeToggle ButtonText:"Skin Paint Mode Toggle" Category:"Skin" internalCategory:"Skin" Tooltip:"Toggle the current skin modifier" SilentErrors:(Debug != false) ( on isVisible return ( (classof(modPanel.GetcurrentObject())) == Skin) on isEnabled return ( (classof(modPanel.GetcurrentObject())) == Skin) on execute do ( skinmod = modPanel.GetcurrentObject() if (skinops.GetNumberBones skinmod) != 0 then ( if subObjectLevel == 0 then ( subObjectLevel = 1 ) skinOps.paintWeightsButton skinmod if skinOps.isInPaintWeightsMode skinmod then ( skinmod.filter_vertices = on ) else ( skinmod.filter_vertices = off ) ) ) )