Defining what can or cannot be done for a customer

I've been thinking about creating ticket categories and sub level categories as a way to tell if we can, or cannot do certain work for a customer. That means controlling permissions allowing only certain categories to be assigned to specific customers. Is that a good approach or feasible approach to maintain long term?

The other method I was thinking is to create a dynamic SQL lookup, so we define for each customer what we don't do out of our whole list of categories, then show a notification on the ticket stating if that work can or cannot be done for a specific customer.

I'm not sure which approach works best, or if there are better ways to manage this than these 2 methods.

The end goal is to allow a tech to know in a few seconds what works is allowed for each customer, based on the ticket category. Let's say a category like Client Apps > Sage 50 can be supported for customer A, but Network > Switches cannot be supported for customer A.