Hi Marc and Timo,
Thanks for using our plugins. It is not currently, a feature to select a category or specify a category for a Facebook imported event. We are in the process of updating the API to the latest version and then will be looking to add new features such as this.
If you would like to request that feature please head to our UserVoice Page and add your own or upvote that feature as they will increase the chances of it being added to a future version.
http://tribe.uservoice.com/forums/195723-feature-ideas
Otherwise I do not have any coding to help out on this.
Let me know if you have any follow up questions.
Thanks