How to link system text templates to multilevel categorization?

Good day all,

We have implemented ITSM (SMIN) for our customer. For the users, we developed several system text templates and multilevel categorization. Is there any solution how to link system templates to categories? I tried to search this configuration in Rule policies and BRFplus but no chance.

The scenario is: when user selects category, system inputs system text template in the rich text editor.