We have not made changes to this API and you can access RowCount, ColumnsCount directly from RadGridView control or from MasterTemplate:
radGridView1.RowCount = 10;
radGridView1.ColumnCount = 10;
radGridView1.MasterTemplate.RowCount = 10;
radGridView1.MasterTemplate.ColumnCount = 10;
If you have other questions, do not hesitate to contact me again.
the Telerik team