We have a requirement where in once the products are imported under /etc/commerce/products/xxx, creation of category and product pages has to be automated.
AEM provides Catalog Blueprints where we have to manually structure the categories, map the templates, clientlibraries, tags etc., and when we click on "Create Catalog" button manually AEM will create the appropriate pages.
Instead this manual process, is there any API provided by AEM to create catalog/rollout catalog changes to generate/update pages.
There is no such API's available in AEM which can solve your problem. You need to create custom tools in order to achieve creating catalog template, blueprint & product pages automatically (Through the API).
I do have these tools for one of my project. May not be as generic as you want, However, things are easier when you use them.