Change StringFormat during Runtime

Question

I have the following Scenario where I want to change the StringFormat of a DataGridTextColumn on runtime. On my DataGrid I have also a DataGridTemplate with a Button inside. When I press the Button I want to change the StringFormat from two decimal places to zero decimal places. How can I do that? I have already tried working with Styles and Dynamic Resources but nothing is working so far. This Code happens in my AutogenerateColumns-Event. DGC is the current column.

DataTrigger t = new DataTrigger();
                        t.Binding = new Binding("Weight");
                        t.Value = 0;
                        Setter s = new Setter();
                        s.Property = DataGridCell.ContentStringFormatProperty;
                        s.Value = new Binding(null) { StringFormat = "N02" };
                        t.Setters.Add(s);

                        Sty.Triggers.Add(t);
                        DGC.CellStyle = Sty;