Service monitoring - previous services.service_message

I have a case where the current “service monitor via nagios plugins”-feature could be improved by having access to the previous services.service_message.

check_http is useful for reporting the current state of the webserver, accessibility of resources, and also the validity of the SSL certificate. But: there is no way to set up alerts to catch changes from the previous service poll, as long as the state of the webserver doesn’t change. We can only trigger on something the nagios plugin considers a problem right now.

If we have access to the previous service_message, we can also use the same plugin to detect if a document has changed:
HTTP OK: HTTP/1.1 200 OK - 134258 bytes in 0.692 second response time

(Not quite an md5 sum, but at least something.)

How much work would it be to save the previous services.service_message to services.service_message_prev?