you might need to put "10" or '10'
mc.mcCntlSetPoundVar(inst, mc.SV_HEAD_SHIFT_Y, "10")
mc.mcCntlSetPoundVar(inst, mc.SV_HEAD_SHIFT_Y, '10')
or just change this mc.mcCntlSetPoundVar(inst, mc.SV_HEAD_SHIFT_Y, 10)
to this
YShift = 10
mc.mcCntlSetPoundVar(inst, mc.SV_HEAD_SHIFT_Y, YShift)