As it is not supported directly through public API of the grid, you have to manually call grid.iUCDate.update ( ) where grid is pqgrid javascript instance obtained by
$grid.data("paramqueryPqGrid"); or $grid.pqGrid( 'instance' );
grid.iUCData.update({
rowData: rowData,
dataIndx: dataIndx,
oldVal: oldVal,
newVal: newVal
})