AWS Chatbot是一种与Slack集成的AWS服务，可以通过它来监控和操作AWS资源。要自定义AWS Chatbot通过Slack发送的消息，需要在AWS Console中创建一个新的通知，然后使用API Gateway和Lambda函数创建一个新的AWS Chatbot事件处理程序。下面是一个示例Lambda函数，用于自定义Slack消息：

import json
import boto3
from botocore.vendored import requests

SLACK_WEBHOOK_URL = "https://hooks.slack.com/services/"

def lambda_handler(event, context):
    message = {
        "text": "This is a custom message from AWS Chatbot",
        "attachments": [
            {
                "fallback": "Upgrade your Slack client to enjoy this feature.",
                "color": "#36a64f",
                "pretext": "Optional text that appears above the attachment block",
                "author_name": "Bobby Tables",
                "author_link": "http://flickr.com/bobby/",
                "author_icon": "http://flickr.com/icons/bobby.jpg",
                "title": "Slack API Documentation",
                "title_link": "https://api.slack.com/",
                "text": "Optional text that appears within the attachment",
                "fields": [
                    {
                        "title": "Priority",
                        "value": "High",
                        "short": False
                    }
                ],
                "image_url": "http://my-website.com/path/to/image.jpg",
                "thumb_url": "http://example.com/path/to/thumb.png",
                "footer": "Slack API",
                "footer_icon": "https://platform.slack-edge.com/img/default_application_icon.png",
                "ts": 123456789
            }
        ]
    }

    response = requests.post(SLACK_WEBHOOK_URL, data=json.dumps(message))
    print(response.status_code)

在此示例中，创建了一个Slack消息，包括文本，附件以及附件中的各种元素。消息通过POST请求发送到Slack Webhook URL。替换上述代码中的SLACK_WEBHOOK_URL变量为你的Slack webhook URL，然后保存并创建AWS Lambda函数。最后，将该Lambda函数添加到AWS Chatbot的事件处理程序中。

这样，当AWS资源触发事件时，AWS Chatbot会调用Lambda函数，该函数将自定义Slack消息发送到指定的Slack频道中。