There is an option in the document properties>image quality that says use isometric, zoom to fit for document preview. If you want to set the view yourself you need to deselect this option set the view for the part then save it this will make your thumbnail look the way it was saved
The same still holds true from 2007. There is still no way to change the thumbnail
image other then rotating the model and re-saving it.
Now what might be useful to you is in the model if you rotate the model around
you can save those orientations by hitting the space bar and then saving those views.
Then you can grab screen shots of the different views. Not sure if that would help you, but it is a suggestion.
I think it is actually worse than Scott says. The thumbnail image doesn't get saved every time you save your file. SolidWorks has its own internal logic that decides when the thumbnail image gets saved and you have no control over it. So you will have to keep saving your part with the chosen view shown until SolidWorks decides the time is right. But if you go back to some other view when you save, you will never know when SolidWorks will decide to save the thumbnail image with that view.
The better option might be to have a macro with option to set the view orientation and save file.
This is just a cheap trick, but it works.... (maybe someone can make a macro for this, pls)
I'm guessing this is for assembly files:
-Open your file
-Choose the view you want
-Click spacebar and update isometric view
-Add a new part (just pick random)
-Delete the (random) part
Wow, that fix is so simple it's scary (BUT - you actually don't have to save after adding the new part, because SolidWorks rebuilds after you do, so that step can be skipped). Plus it's the only idea here that actually worked. Great job!
Now, why can't Dassault just add a checkbox that says "update thumbnail" when you click Save As...?
Changing the graphics resolution in your document settings will cause SW to regenerate a new thumbnail. Goto tool options document setting and move the slider for the image quality then rebuild/safe. That should update the thumbnail for the file.