code.cs

private void ApplyMaskedString(RibbonItemCollection ribbonItems, dynamic data)
{
    // flatten data object in case of an array
    if (data.GetType() == typeof(JArray))
        data = data[0];

    // loop through all ribbon items in the "insert merge fields" menu
    foreach (Control ribbonButton in ribbonItems)
    {
        // in case, the item is a drop-down, call ApplyMaskedString
        // recursively with a new data object
        if (ribbonButton is RibbonMenuButton)
        {
            ApplyMaskedString(
                ((RibbonMenuButton)ribbonButton).DropDownItems,
                data[ribbonButton.Text]);
        }
        // in case it is a merge field insert button
        else if (ribbonButton is RibbonButton)
        {
            // and it is not a separator or title
            if (!ribbonButton.Name.StartsWith("TXITEM_"))
            {
                // get the data from the first data row
                var dataValue = data[ribbonButton.Text];

                if (dataValue == null)
                    continue;

                if (dataValue.GetType() == typeof(JValue))
                { 
                    // change the actual text
                    ribbonButton.Text = dataValue.Value;
                }
            }
        }
    }
}