If you want to change the properties of the catalog in Sitecore Commerce 9 you'll find there is no information in the developer's guide or the DevOps guide.

Fortunately there is a knowledge base article that describes the steps on how to extend the catalog: https://kb.sitecore.net/articles/083614

The article describes how you can extend the default schema for Sellable Items (Products), Categories and Catalogs programmatically. It also describes how you can add the relevant blocks so the extended catalog schema can be viewed and edited in the business tools.