Yes, it is possible to add a tooltip on the cells. I am attaching an example which shows how you can achieve the desired behavior. However, this demo uses the MouseMove event to track the position of the mouse and visualize the tooltip and, because this event is triggered pretty often, this could decrease the performance of the control. You could optimize the scenario using a timer to delay the showing of the tooltip. This timer can check how often the UpdateUI method is invoked.
When it comes to cell templates, RadSpreadsheet is designed to visualize spreadsheet documents and it is not intended to allow changing the template of the cell. Depending on your requirements, however, you can implement a custom CellEditUILayer and change the editor of the cells. There is an example on how to achieve that in this forum post
Hope this is helpful.
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