Yes, you can customize notification templates by using your Dashboard.
Click "Templates" in the Left Navigation Menu. Click "Add Template" on the next page:
Then you will be able to create new templates for email, SMS or Slack notifications. Be sure your new template has a name, and then hit "Create Template":
If you do not want to share your new template with other properties in your company, do not tick the box that says "Share this template with other properties." Only tick the box that says "Make this the default":
You can also edit or delete existing templates by clicking the little pencil next to any template. You can also delete an existing template by clicking the little x next to it: