Amazon ElasticSearch (OpenSearch) Advanced Configuration

In this doc article, I saw only a couple of settings can be adjusted via the advancedOptions param (we're still on ES OSS, version 7.10): https://docs.aws.amazon.com/opensearch-service/latest/developerguide/supported-operations.html#version_7_10

So, my question is: can users adjust other settings? The particular setting I'm interested in is the indices.memory.index_buffer_size.

A quick google search gave me the impression that other settings cannot be adjusted, except maybe if the AWS Support Team is contacted, and then the new settings can be applied by AWS.

Would like to know more on this.

Thanks!