Inside "CreateFullScreenDisplay" procedure calls
&nbsp&nbsphr := m_pDD.SetDisplayMode( dwWidth, dwHeight, dwBPP, 0, 0 );
So if you clone this procedure (CreateFullScreenDisplay) you can modify it to something like this:
&nbsp&nbsphr := m_pDD.SetDisplayMode( dwWidth, dwHeight, dwBPP, MyNewRefreshRate, 0 );