Hi Ruslan,
Thank you for your interest in Syncfusion Products.
We regret to let you know that it is not possible to set the selected index via client side mouse over function and added to the SelectedRecord collection. GridGroupingControl provides support for different types of selection modes. Depending upon the selection mode, the selection style can be varied. Please refer the on line sample illustrating different selection mode and getting added to that SelectedRecord collection.
http://samples.syncfusion.com/ASPNET/7.2.0.37/web/grid.grouping.web/samples/3.5/ColumnOrRows/RowSelectionModes/cs/rowselectionmode.aspxPlease let me know if you have any concerns.
Thanks,
Rekha