How to create animated thumbnail using part of movie ( decreasing lenght of project )

1- Create part of principal movie in Vegas (for trailer)and save, p.ex: Principal-Movie-Trailler-1
2- Open DVDA and drag previous rendered movie trailer to MAIN MENU ( DVDA will create a thumbnail)...animated or not...
3- Double click on Thumb, open timeline.
4- Drag the Principal-Movie ( on media explorer ) to timeline ( the previous "Principal-Movie-Trailler-1" will dessapear)

When you watch the PREVIEW, the thumbnail on MAIN MENU will be "Principal-Movie-Trailler-1" but the link will show the "Principal-Movie"