No, I don't know of a way to modify a file from SWPDM outside of changing variables. If you could change the part configuration used in an assembly you would most likely have to check the file out. That would mean that you would have to have something other than a viewer license as viewers cannot checkout.
I think the only option would be to have configurations in the assembly that used the desired part configurations. Then the person that was viewing the file could just use the Contains tab to switch which assembly configuration they are looking at. I don't see a way to see a configuration in the preview tab or in eDrawings for that matter. All I can see is the assembly configuration that was active when I saved last.
If you save as an eDrawings file you can change configurations in eDrawings but not in the SWPDM preview tab.