Calling 'loadData' method for a special node is not allowed. But the user can remove all children and then append some new nodes for that node. Here is the test code to demonstrate how to do this.
function reloadData(data){
var tg = $('#test');
var node = tg.treegrid('getSelected');
if (node){
var cc = node.children||[];
while(cc.length){
tg.treegrid('remove', cc[0]['id']);
}
tg.treegrid('append', {
parent: node.id,
data: data
});
}
}