Although I'm not sure I fully understood your scenario and requirement, I believe you can handle the Searching event of the control, cancel it, and perform your custom filtering.
private void RadGridView_Searching(object sender, Telerik.Windows.Controls.GridView.GridViewSearchingEventArgs e)
if (e.SearchText.ToString() == "SomeText")
e.Cancel = true;
Can you please let me know if such an approach would work for you or if I have misunderstood your requirement in any way?
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