You can add buttons,separators and custom buttons programmaticly using the Add method the buttons are displayed in the same order as they are added:

rtbIngress.toolbar.Add(rtbIngress.Cut);
    rtbIngress.toolbar.Add(rtbIngress.Copy);
    rtbIngress.toolbar.Add(rtbIngress.Paste);
    rtbIngress.toolbar.Add(rtbIngress.PasteText);
    rtbIngress.toolbar.Add(rtbIngress.PasteWord);
    rtbIngress.toolbar.Add(rtbIngress.Separator);
    rtbIngress.toolbar.Add(rtbIngress.Undo);
    rtbIngress.toolbar.Add(rtbIngress.Redo);
    rtbIngress.toolbar.Add(rtbIngress.Separator);
    rtbIngress.toolbar.Add(rtbIngress.AbsolutePosition);
    rtbIngress.toolbar.Add(rtbIngress.Char);
    rtbIngress.toolbar.Add(rtbIngress.InsertText);
    rtbIngress.toolbar.Add(rtbIngress.Separator);

Regards,

Thomas