As described in the AWS docs there are platform hooks for elastic beanstalk EBS for the deployment process: https://docs.aws.amazon.com/elasticbeanstalk/latest/dg/platforms-linux-extend.html
But what can I do, to run a script each time someone changes the EBS configuration, e. g. an environment property?
If you look at the current docs here: https://docs.aws.amazon.com/elasticbeanstalk/latest/dg/platforms-linux-extend.html, under Platform hooks -> Configuration deployment platform hooks, it explains:
A configuration deployment occurs when you make configuration changes that only update environment instances without recreating them.
And further:
To provide hooks that run during a configuration deployment, place them under the .platform/confighooks directory in your source bundle
So adding a Configuration deployment platform hook in this way should execute each time an environment property is changed.
Unfortunately there is no way to do this currently: https://github.com/aws/elastic-beanstalk-roadmap/issues/15#issuecomment-616843537
