I would need to include specific information in Slack messages sent by Sentry alerts.

You can add tags and notes to Slack messages.

When setting up Slack notifications through your organisation's Alerts tab, you can choose which tags of the event you want to include in the notification:

The alert message will contain all tags(if they exist in the event triggering the alert) and notes. It is currently not possible to add other information or to customise the information in the tag (for example, show only part of the URL present in the URL tag).