The new API would allow some of the default functions to be removed and custom aggregate functions to be added. At the moment the dialog can be modified like this: Public Class MyAggregateOptionsDialog Inherits AggregateOptionsDialog Private availableAggregateFunctions As IList(Of AggregateFunction) = New List(Of AggregateFunction)() From { AggregateFunctions.Sum, AggregateFunctions.Count, AggregateFunctions.Average, AggregateFunctions.Max, AggregateFunctions.Min, AggregateFunctions.Product, AggregateFunctions.StdDev, AggregateFunctions.StdDevP, AggregateFunctions.Var, AggregateFunctions.VarP, New SqrtSumAggregateFunction() } Public Overrides Sub LoadSettings(aggregateDescription As PropertyAggregateDescriptionBase) MyBase.LoadSettings(aggregateDescription) Dim listAggregateFunctions = DirectCast(Me.GetType().BaseType.GetField("listAggregateFunctions", BindingFlags.NonPublic Or BindingFlags.Instance).GetValue(Me), RadListControl) listAggregateFunctions.DataSource = availableAggregateFunctions End Sub End Class