VSB gives you the option (under Documetation) to give the Theme a name. But at least for me this doesn't seem to work. All designs are listed as Windows-Aero or "-Basis" (not BasiC because my language is German, maybe this is the problem...).
Do I have to edit the .msstyles.mui file?
There is no .msstyles.mui files when you use VSB. It embeds it within the theme. Also if you change the Documentation it's likely to not show in the default Vista theme selector.