Is this possible in wpmu and bp?
Is this possible in wpmu and bp?
Go into the backend of that blog and pick a different theme.
If you don't want the theme available to other users, disable it in Site Admin -> themes.
enable it for just that blog by going to Site Admin -> Blogs, then Edit. On the right is a list if disabled themes. Hit the checkbox & save.
then you'll see that theme available in the Appearance menu in the backend of that particular blog, and ONLY that blog.