Yup
In a normal VC army your vampires will default to VonCarstein, but you can switch that with the options on the Blood tab (just above the standard options tab on the right). The alternate rule sets are separate army lists which are customized out along particular themes. They are similar to the basic VC list, but not quite the same in many cases. They can be fun, as most of them have some interesting special rules, but they aren't considered 'official' for tournaments and such.