private void BillingEngine_DuringSave(object sender, MercatorUi.Engine.Gescom.BillingEngine.DuringSaveEventArgs e)
{
    MercatorUi.Engine.Gescom.BillingEngine billingEngine = (MercatorUi.Engine.Gescom.BillingEngine)sender;
    e.MercatorSqlCommand.CommandText = "update ...";
    e.MercatorSqlCommand.Parameters.AddWithValue("@param", "...");
}