So, in our Bizfx we defined a catalog Catalog containing two categories, Category_1 and Category_2.
In Content Editor the catalog displays the items from both categories with CommerceProduct template. When we change the Product template field to of the Catalog to our custom template Template_A, all the items are assigned the Template_A
Now, what we need is to set Product template on category level, not catalog level. In other words, we want Content Editor to show items under Category_1 as Template_A, and items under Category_2 as Template_B