I didn’t mention that, I was talking about adding an option to Hibernate Search. I understand the problem is that the service is hardcoded. Until now that was the only relevant value, so… 
Yes, please open an issue on Jira.
Not that I know. Thought I guess you can copy/paste the code of hibernate-search-backend-elasticsearch-aws into your project and make the necessary changes, if your project complies with Hibernate Search’s source code license.