custom message in the SNS

I am currently storing the commit ID in a file named (commit) within the file that is updated to the S3. Is there a way to read the file so that it can be used within the SNS payload and I could I relate the `deploy-id` with the `commit-id` when sending alerts for example via slack.

Currently the alerts look like this:
```
[test] - Deployment d-705FE8ZY4 app-title : i-0d910a1c70be24407 Succeeded
ApplicationStop: Succeeded
DownloadBundle: Succeeded
BeforeInstall: Succeeded
Install: Succeeded
AfterInstall: Succeeded
ApplicationStart: Succeeded
ValidateService: Succeeded
```

But I haven't found how to use/read the commit file that is within the app.tgz so that I could use is as the title, or wondering if instead of triggering automatically the pipeline by updating the file in S3, is there a way to trigger the deploy via an API call in where I could there add a custom payload (pass the commit Id) and use it?