Unfortunately the desired functionality is not supported into the RadGrid. Yes, you can handle the PreRender event and iterate over all columns, you can access the cells by their indexes and find the values into them, however you cannot insert rows and columns dynamically, because the RadGrid is a data bound control and it shows the data from the data source. So, in your case you need to modify the data source to which the RadGrid is bound. Then on PreRender event you can apply different styles to the totals and grand total rows/columns. For example you can create an in-memory DataTable which contains calculated totals and grand total rows/column and use it as data source of the RadGrid.
I hope this helps.
the Telerik team
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