is it possible to change the highlited shape when the diagram loads.? Any help is much appreciated
Do you mean: “How do I change a shape dynamically at any time after the diagram has loaded?”? Because until it has loaded there is nothing to change.
If so, the page GoJS Data Binding -- Northwoods Software covers what you should do. Basically, use a Binding on one or more of the properties that you want to change. Then when you want to change it, start a transaction, modify the model data property or properties by calling model methods, and then commit the transaction.
If not, I’m not sure what you want to do. Maybe you just want to load different data each time. The Bindings will ensure that the GraphObject properties correspond to the data values.