Customizing Amazon SNS email notifications

I don't believe any customization is possible. For custom e-mails you should use Amazon SES instead. You would however need to manage unsubscribes yourself.

You can't change the sender (AWS Notifications), but you can change the body with Lambda or custom code running on your EC2 or on-premise instances. Here's Python code for sending a custom SNS message:

import boto3
def lambda_handler(event, context):
    message = "My Custom Message"
    client = boto3.client('sns')
    response = client.publish(
        TargetArn="YOUR_ARN",
        Message=message,
        MessageStructure='text',
        Subject='My Subject',
    )