welcome to the community. Just a few tips beforehand: Always choose a matching category for your questions, #community doesn’t fit here, so I’ve moved it to #icinga-2-core.
In terms of your question, I’m not sure about the purpose of “classification”. Is that for views on your web interface, a specific notification rule, or something else? The most simplest solution for a preliminary classification would be “host groups”, where these hosts can be a member of.
With the power of assign where expressions, this can be achieved either with the host name pattern, or just by using custom variable providers in the host object.