How to change the "drop indicator" to "no-drop indicator" dynamically while dragging?

Hi,
We are using Smart Gwt-4.1p (23rd May 2014)
Browser: IE10, 11, Google Chrome:37.0.2062.124 m

We are using the TreeGrid and ListGrid in our project. We are trying to put the drag and drop feature from ListGrid to TreeGrid. We have achieved to drag and drop the records. But, we would like to show the "no-drop indicator" for few nodes in the tree ie.., the treeGrid should not allow drop on few levels in the tree. So now, How can we change the indicators from "drop indicator"(allowed) to "no-drop indicator"(disallowed) and vice versa dynamically?

Any suggestions would be appreciated.