You can customize the actions in the filtering ComboBox.
1. I would recommend you to run through this article to get the keys for actions in ComboBox.
2. The FilterOperatorsLoading event (that was added Q3 2011) allows you to remove the available filter operators. Please refer to the Events section in this help article.
I hope that this is what you need.
All the best,
the Telerik team
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