Rockin, you can import a classification.config file from the "Custom Attack Editor" by selecting the "File" | "Import" | "Snort Rules" menu. Then you will be prompted for the file name and .conf and .config files are one of the file types that you can choose from. You can import your classifications that way. Hope this helps.
Classtypes are essentially used to translate to a priority (severity), and as far as I know you need one or the other so the manager knows if you want to treat this attack as high, medium or low severity. I have certainly been on sites that dont import any config files and just specify the required priority in the snort rule body.
Saying that, however - config files are the way to go as LavonF suggests :-)