Unfortunately, such functionality is not possible with the current WebAqua. A feature request has been submitted to the developer for programmatic animation trigger in WebAqua.

We will inform you if there is any update or progress regarding the feature request.

Could you provide us with a running sample for what you are trying to do, or provide us with a snippet code for the event handler where you are trying to change the WebCombo data source.

This will allow us to replicate the scenario you are facing more accurately.

In order to analyze the issue we need to be able to replicate the issue in our environment.

I have prepared a simple sample page with the scenario you described, custom object bound to ObjectDataSource and WebGrid is bound to the ObjectDataSource. The custom object has already been available in our WebGrid sample. Feel free to modify the sample or the custom object in order to replicate the issue. 

You could add a new cell during InitializeDataSource server side event in the WebGrid datasource and fill in the value of the cell during InitializeRow server side event. Here is the snippet to fill in the FullName cell with FirstName and LastName cell value:

protected void wgTest_InitializeRow(object sender, RowEventArgs e)
{
    if (e.Row.Type == RowType.Record)
    {
        e.Row.Cells.GetNamedItem("FullName").Text = String.Join(" ",
            new string[] { e.Row.Cells.GetNamedItem("FirstName").Text, e.Row.Cells.GetNamedItem("LastName").Text});

        e.Row.Cells.GetNamedItem("FullName").Value = String.Join(" ",
            new string[] { e.Row.Cells.GetNamedItem("FirstName").Text, e.Row.Cells.GetNamedItem("LastName").Text });
    }
}

Other method would be to modify the select query so you will get the merge cells. Again we show how to select a FullName by merging FirstName and LastName field

SELECT EmployeeID, FirstName, LastName, FirstName + ' ' + LastName AS FullName FROM [Employees]

If the proposed solution does not fit for your scenario, please elaborate your scenario.

In order to automatically set the WebCombo value to the shown dropdown item you will need to use EntryMode AutoComplete instead of InstantLookup.

Regarding the missing WebCombo text, in such scenario you will need to fill the virtual column (in this case FullName) as you set the value to the WebCombo. The InitializeRow server side event will be invoked when you show the WebCombo dropdown, in your scenario the InitializeRow will not be triggered.

Other suggestion regarding your scenario would be modifying the select query from the database. Instead of SELECT UserID, FirstName, LastName FROM [Users], please use SELECT UserID, FirstName, LastName, FirstName + ' ' + LastName AS FullName FROM [Users]