You will need to add a new ChartPivotDataConfig in the chart data collection and a new ChartPivotFilterConfig in the char category collection. Here is the snippet, I'm using lambda expression to insert the property in the object:

Protected Sub WebGrid1_ChartImageProcessing(ByVal sender As Object, ByVal e As ISNet.WebUI.WebGrid.Chart.WebGridChartEventArgs) Handles WebGrid1.ChartImageProcessing
    e.ChartConfig.ChartDataCollection.Add(New ChartPivotDataConfig() With {.DataMember = "ID"})
    e.ChartConfig.ChartCategoryCollection.Add(New ChartPivotFilterConfig() With {.DataMember = "Interest"})
End Sub

function UpdateGrid()
{
    var wgTest = ISGetObject("wgTest");
    var row = wgTest.RootTable.GetRow(2);
    var cells = row.GetCells();
    var interestCell = cells.GetNamedItem('Interest');

    interestCell.SetValue("1");
    row.Select();
    interestCell.ActivateEdit();
    
    row.SetDataChanged();
    row.Update();

    wgTest.MarkEdit();
}

function wgTest_OnEnterEditMode(controlId, tblName, editObject)
{
    var wgTest = ISGetObject(controlId);
    var selIndex = editObject.element.selectedIndex
    var selText = editObject.element.options[selIndex].text;

    editObject.ToCellObject().SetText(selText);
}

Unfrotunately such scenario has not been supported by WebScheduler. 

However, after discussing this issue with the developer, a workaround would be to hide the event which shown in the holiday date. This could be achieved using OnEventBound client side event handler by comparing the event date and holidays, if it match set the css style of the event so the event will be hidden. Here is the snippet:

function WebScheduler1_OnEventBound(controlId, evt)
{
    var sched = ISGetObject(controlId);

    var evtDay = [evt.StartTime.getDate(), evt.StartTime.getDay(), evt.StartTime.getFullYear()].join("/");

    for (var i = 0; i < sched.Holidays.length; i++)
    {
        var hDate = sched.Holidays[i].Date;
        var hDateStr = [hDate.getDate(), hDate.getDay(), hDate.getFullYear()].join("/");
        if (evtDay == hDateStr)
        {
            evt.Element.style.display = "none";
        }
    }
}

You could retrieve the selection of the HTML element the command executed on using the GetSelectionParentNode function. For your scenario, you try using the OnAfterExecCommand event handler and rewrite the HTML element so the style tag will be outside of the SPAN with the type attribute mailmerge. 

Here is the snippet for Bold command:

function WebTextEditor_OnAfterExecCommand(controlId, action)
{
    var WebTextEditor = ISGetObject(controlId);
    var selection = WebTextEditor.GetSelectionParentNode();
    
    if(selection.parentElement.getAttribute("type") == "mailmerge")
    {
        switch(action)
        {
            case "Bold":
                var oNew = document.createElement("strong");
                selection.parentElement.parentElement.insertBefore(oNew, selection.parentElement);
                oNew.appendChild(selection.parentElement);

                selection.parentElement.innerHTML = selection.parentElement.innerHTML.replace(/<strong>/i, "").replace(/<\/strong>/i, "");
                break;
        }
    }
}