I found this post but at the end it suggests making changes to the registry which scares me a little bit. Is there a better way to do this? Is modifying the registry in this case "normal"?
I think you cannot avoid the change in registry because.. Along with ULS logs the SharePoint also puts an entry into an event log. You can see your custom category into an event log also. And Windows stores Event Log categories in Registry.
A better way to do is to register it along with your FEATURE as documented here: http://jbaurle.wordpress.com/2011/01/16/how-to-implement-a-custom-sharepoint-2010-logging-service-for-uls-and-windows-event-log/