There are often several ways of doing the same thing with LDSD, so I'd certainly try out Andy s suggestions and see what works best for you.
If you want to preset your category you'd probably best using a template to set the value and then hide the attribute as you have already done. I've often set the source of an incident to be mail, self service, and so on using this method so you are tagging data that is useful, but doesn't need to be visible.
Depending on the version you are using make sure you save often. If you window goes blank and any time when you are desiging it, just exit and do not save